Google Coding Interview Questions: 609 Tagged Problems

609 coding problems tagged Google — 107 easy · 363 medium · 139 hard — with solutions in 13 languages. Plus a 4-week study plan by topic.

Problems: 609
By difficulty: 107 easy · 363 medium · 139 hard
Languages: JavaScript, TypeScript, Python, Java, C++, C, C#, Go, Kotlin, Swift, Rust, PHP and Ruby
Cost: Free on every plan; sign in to run and submit

609 problems the CodeKairo catalogue tags as commonly asked in Google's coding rounds — 107 easy, 363 medium and 139 hard — each judged by hidden tests in 13 languages. The most common topics among them are Arrays (372), Dynamic Programming (155) and Strings (150). At 55% of the catalogue the tag is a broad net rather than a shortlist; the pattern below is the narrower place to start. CodeKairo's Google — Online Assessment mock covers the Google online assessment pattern for university candidates: two coding problems, one clock, and nothing else. The tag is the catalogue's own annotation of where a problem tends to come up — not a list published by Google, which CodeKairo is not affiliated with.

Google study plan by topic

40 of the 609 problems tagged Google over 4 weeks, about 21 h 20 min of solving, grouped by technique in the order they build on each other — Arrays, Strings, Hash Table and Counting and 23 more. It ends with the Google — Online Assessment mock.

Week 1: Arrays, Strings, Hash Table +5

12 problems on Arrays, Strings, Hash Table, Counting, Math, Two Pointers, Sliding Window and Prefix Sum, easiest first within each topic.

Max Consecutive Ones Easy
Detect Capital Easy
Jewels and Stones Easy
Majority Element II Medium
Minimum Number of Frogs Croaking Medium
Factorial Trailing Zeroes Medium
Merge Strings Alternately Easy
String Compression Medium
Minimum Difference Between Highest and Lowest of K Scores Easy
Maximum Number of Vowels in a Substring of Given Length Medium
Find Pivot Index Easy
Find the Highest Altitude Easy

Week 2: Sorting, Binary Search, Stack +4

11 problems on Sorting, Binary Search, Stack, Monotonic Stack, Matrix, Simulation and Greedy, easiest first within each topic.

Largest Perimeter Triangle Easy
Third Maximum Number Easy
Count Pairs Whose Sum is Less than Target Easy
Minimum Common Value Easy
Count Negative Numbers in a Sorted Matrix Easy
Longest Valid Parentheses Hard
Number of Visible People in a Queue Hard
Unique Paths II Medium
Game of Life Medium
Longest Palindrome Easy
Increasing Triplet Subsequence Medium

Week 3: Heap, Bit Manipulation, Bitmask +7

12 problems on Heap, Bit Manipulation, Bitmask, Number Theory, Combinatorics, Backtracking, Graph, Breadth-First Search, Topological Sort and Union Find, easiest first within each topic.

Week 4: Dynamic Programming, Game Theory

5 problems on Dynamic Programming and Game Theory, easiest first within each topic.

Delete and Earn Medium
Best Time to Buy and Sell Stock III Hard
Distinct Subsequences Hard
Palindrome Partitioning II Hard
Stone Game III Hard

Finally: the timed test

Sit the Google — Online Assessment mock under the clock — the coding problems are only one part of the round.

Take the Google — Online Assessment mock

Google test patterns

Google — Online Assessment pattern guide and timed mock

All problems tagged Google

Easy (107)

Find the Original Typed String I String
Special Array I Array
Type of Triangle Array, Math, Sorting
Find the Losers of the Circular Game Array, Hash Table, Simulation
Form Smallest Number From Two Digit Arrays Array, Hash Table, Enumeration
Delete Greatest Value in Each Row Array, Matrix, Sorting
The Employee That Worked on the Longest Task Array
Calculate Delayed Arrival Time Math
Most Frequent Even Element Array, Hash Table, Counting
Rearrange Characters to Make Target String Hash Table, String, Counting
Number of Strings That Appear as Substrings in Word Array, String
Circular Sentence String
Number of Senior Citizens Array, String
Find Words Containing Character Array, String
Strong Password Checker II String
Decode the Message Hash Table, String
Count Prefixes of a Given String Array, String
Count Asterisks String
Existence of a Substring in a String and Its Reverse String, Hash Table
Number of Changing Keys String
Find the Encrypted String String, Simulation
Count the Number of Incremovable Subarrays I Array, Two Pointers, Enumeration
Modify the Matrix Array, Matrix
Find the Power of K-Size Subarrays I Array, Sliding Window
Number of Bit Changes to Make Two Integers Equal Bit Manipulation
Find the XOR of Numbers Which Appear Twice Array, Hash Table, Bit Manipulation
Apple Redistribution into Boxes Array, Greedy, Sorting
Number of Beautiful Pairs Array, Hash Table, Math
Check if Array is Good Array, Hash Table, Sorting
Neither Minimum nor Maximum Array, Sorting
Alternating Groups I Array, Sliding Window
Distribute Elements Into Two Arrays I Array, Simulation
Minimum Sum of Mountain Triplets I Array, Prefix Sum
Find the Integer Added to Array I Array, Math
Minimum Operations to Exceed Threshold Value I Array
Kids With the Greatest Number of Candies Array
Separate the Digits in an Array Array, Simulation
Find the Child Who Has the Ball After K Seconds Math, Simulation
Minimum Time Visiting All Points Array, Math, Geometry
Split the Array Array, Hash Table, Counting
Find Champion II Graph
Find Champion I Array, Matrix, Graph
Minimum Amount of Time to Fill Cups Array, Greedy, Math
Kth Missing Positive Number Array, Binary Search
Minimum Recolors to Get K Consecutive Black Blocks String, Sliding Window
Valid Word Abbreviation String, Two Pointers
Rank Transform of an Array Array, Hash Table, Sorting
Maximum Odd Binary Number String, Greedy
Distribute Money to Maximum Children Math, Greedy
Find the Winning Player in Coin Game Math, Game Theory
Check If It Is a Straight Line Array, Math, Geometry
Add to Array-Form of Integer Array, Math
Permutation Difference between Two Strings String, Hash Table
Remove Palindromic Subsequences String, Two Pointers
Number of Different Integers in a String String, Hash Table
Greatest Common Divisor of Strings String, Math
Verifying an Alien Dictionary Array, String, Hash Table
Unique Morse Code Words Array, String, Hash Table
Long Pressed Name String, Two Pointers
Maximum Difference Between Increasing Elements Array
Replace Elements with Greatest Element on Right Side Array
X of a Kind in a Deck of Cards Array, Math, Number Theory
Fair Candy Swap Array, Hash Table
Find the Difference Hash Table, String, Bit Manipulation
Binary Gap Bit Manipulation
Counting Bits Dynamic Programming, Bit Manipulation
Number of 1 Bits Divide and Conquer, Bit Manipulation
Largest Perimeter Triangle Array, Math, Greedy
Assign Cookies Array, Two Pointers, Greedy
Projection Area of 3D Shapes Array, Math, Geometry
The K Weakest Rows in a Matrix Array, Binary Search, Sorting
Count Negative Numbers in a Sorted Matrix Array, Binary Search, Matrix
Flipping an Image Array, Two Pointers, Matrix
Toeplitz Matrix Array, Matrix
Number of Arithmetic Triplets Array, Hash Table, Two Pointers
Minimum Common Value Array, Hash Table, Two Pointers
Count Pairs Whose Sum is Less than Target Array, Two Pointers, Binary Search
Rearrange Spaces Between Words String
Special Array With X Elements Greater Than or Equal X Array, Binary Search, Sorting
Array Partition Array, Greedy, Sorting
Minimum Difference Between Highest and Lowest of K Scores Array, Sliding Window, Sorting
Shortest Distance to a Character Array, Two Pointers, String
Merge Strings Alternately Two Pointers, String
Count Binary Substrings Two Pointers, String
Unique Email Addresses Array, Hash Table, String
Rotate String String, String Matching
Buddy Strings Hash Table, String
License Key Formatting String
Jewels and Stones Hash Table, String
Longest Palindrome Hash Table, String, Greedy
Repeated Substring Pattern String, String Matching
Detect Capital String
Reverse Vowels of a String Two Pointers, String
Third Maximum Number Array, Sorting
Max Consecutive Ones Array
Sum of All Odd Length Subarrays Array, Math, Prefix Sum
Find the Highest Altitude Array, Prefix Sum
How Many Numbers Are Smaller Than the Current Number Array, Hash Table, Counting Sort
Find Pivot Index Array, Prefix Sum
Set Mismatch Array, Hash Table, Bit Manipulation
N-th Tribonacci Number Math, Dynamic Programming, Memoization
Add Strings Math, String, Simulation
Plus One Array, Math
Add Binary Math, String, Bit Manipulation
Power of Three Math, Recursion
Power of Two Math, Bit Manipulation
Happy Number Hash Table, Math, Two Pointers

Medium (363)

Make Three Strings Equal String
Minimum Number of Increments on Subarrays to Form a Target Array Array, Greedy, Dynamic Programming
Find the Winner of an Array Game Array, Simulation
Queries on a Permutation With Key Array, Binary Indexed Tree, Simulation
Corporate Flight Bookings Array, Prefix Sum
Find the Winner of the Circular Game Array, Math, Recursion
Longest Subsequence With Limited Sum Array, Binary Search, Greedy
Partition Array for Maximum Sum Array, Dynamic Programming
Stone Game VII Array, Math, Dynamic Programming
Minimum Number of Work Sessions to Finish the Tasks Array, Dynamic Programming, Bit Manipulation
Count Fertile Pyramids in a Land Array, Dynamic Programming, Matrix
Number of Ways to Divide a Long Corridor Math, String, Dynamic Programming
Maximum Number of Non-overlapping Palindrome Substrings String, Dynamic Programming, Greedy
Count Ways to Group Overlapping Ranges Array, Sorting, Math
Count Number of Ways to Place Houses Math, Dynamic Programming
Count Number of Texts Hash Table, Math, String
Number of Ways to Reach a Position After Exactly k Steps Math, Dynamic Programming, Combinatorics
Delete Characters to Make Fancy String String, Greedy
Count Number of Homogenous Substrings Math, String
Construct String With Repeat Limit Hash Table, String, Greedy
Minimum Number of Steps to Make Two Strings Anagram II Hash Table, String, Counting
Count Vowel Substrings of a String Hash Table, String, Sliding Window
Longest Substring of All Vowels in Order String, Sliding Window
Minimum Deletions to Make String Balanced String, Dynamic Programming, Stack
Minimum Length of String After Operations Hash Table, String, Counting
Minimum Number of Changes to Make Binary String Beautiful String, Greedy
Lexicographically Minimum String After Removing Stars String, Greedy, Heap (Priority Queue)
Count Substrings Starting and Ending with Given Character Math, String, Counting
Sort Vowels in a String String, Sorting
Find the Integer Added to Array II Array, Two Pointers, Sorting
Minimum Operations to Exceed Threshold Value II Array, Heap (Priority Queue), Simulation
Sum of Digit Differences of All Pairs Array, Hash Table, Math
Alternating Groups II Array, Sliding Window
Minimum Sum of Mountain Triplets II Array, Prefix Sum
Count Days Without Meetings Array, Sorting
Water Bottles II Math, Simulation
Determine the Minimum Sum of a k-avoiding Array Array, Math, Greedy
Find the Value of the Partition Array, Sorting
Maximum Value of an Ordered Triplet II Array, Prefix Sum
Process Tasks Using Servers Array, Simulation, Heap (Priority Queue)
Maximum Number of Eaten Apples Array, Greedy, Heap (Priority Queue)
K-th Smallest Prime Fraction Array, Binary Search, Sorting
Find K Pairs with Smallest Sums Array, Heap (Priority Queue)
Maximum Subsequence Score Array, Greedy, Sorting
Total Cost to Hire K Workers Array, Two Pointers, Simulation
Single-Threaded CPU Array, Sorting, Heap (Priority Queue)
Most Beautiful Item for Each Query Array, Binary Search, Sorting
Number of Orders in the Backlog Array, Simulation, Heap (Priority Queue)
Maximum Number of Events That Can Be Attended Array, Greedy, Sorting
The Number of the Smallest Unoccupied Chair Array, Hash Table, Heap (Priority Queue)
Maximal Score After Applying K Operations Array, Greedy, Heap (Priority Queue)
Find the Kth Largest Integer in the Array Array, String, Sorting
Maximum Score From Removing Stones Math, Greedy, Heap (Priority Queue)
Minimum Cost to Connect Sticks Array, Greedy, Heap (Priority Queue)
Find the Safest Path in a Grid Array, Matrix, Binary Search
Number of Ways to Arrive at Destination Graph, Dynamic Programming, Shortest Path
Course Schedule IV Graph, Topological Sort, Depth-First Search
Parallel Courses Graph, Topological Sort, Breadth-First Search
Detonate the Maximum Bombs Array, Math, Graph
The Maze II Array, Matrix, Graph
Open the Lock Array, String, Breadth-First Search
Loud and Rich Array, Graph, Topological Sort
Shortest Path with Alternating Colors Graph, Breadth-First Search
Number of Nodes in the Sub-Tree With the Same Label Hash Table, Tree, Graph
Minimum Fuel Cost to Report to the Capital Tree, Graph, Depth-First Search
Maximum Star Sum of a Graph Array, Graph, Greedy
Count the Number of Complete Components Graph, Union Find, Depth-First Search
Minimum Score of a Path Between Two Cities Graph, Union Find, Depth-First Search
Reachable Nodes With Restrictions Array, Tree, Graph
Largest Plus Sign Array, Matrix, Dynamic Programming
Remove All Ones With Row and Column Flips Array, Matrix, Bit Manipulation
Number of Corner Rectangles Array, Matrix, Math
Magic Squares In Grid Array, Matrix, Simulation
Construct Product Matrix Array, Matrix, Prefix Sum
Maximum Number of Moves in a Grid Array, Matrix, Dynamic Programming
Map of Highest Peak Array, Matrix, Breadth-First Search
Check Knight Tour Configuration Array, Matrix, Depth-First Search
First Completely Painted Row or Column Array, Matrix, Hash Table
Find All Groups of Farmland Array, Matrix, Depth-First Search
Matrix Block Sum Array, Matrix, Prefix Sum
Spiral Matrix III Array, Matrix, Simulation
Where Will the Ball Fall Array, Matrix, Simulation
Maximum Matrix Sum Array, Matrix, Greedy
Minimum Cost Tree From Leaf Values Array, Dynamic Programming, Stack
The Number of Beautiful Subsets Array, Hash Table, Dynamic Programming
Longest Binary Subsequence Less Than or Equal to K String, Greedy, Dynamic Programming
Number of Ways to Select Buildings String, Dynamic Programming, Prefix Sum
Number of People Aware of a Secret Queue, Dynamic Programming, Simulation
Longest Ideal Subsequence Hash Table, String, Dynamic Programming
Stone Game II Array, Dynamic Programming, Prefix Sum
Predict the Winner Array, Dynamic Programming, Recursion
Count Ways To Build Good Strings Dynamic Programming
Longest Arithmetic Subsequence Array, Hash Table, Dynamic Programming
Coin Change II Array, Dynamic Programming
Minimum Impossible OR Array, Bit Manipulation, Brainteaser
Minimum Additions to Make Valid String String, Greedy, Dynamic Programming
Partition String Into Substrings With Values at Most K String, Greedy, Dynamic Programming
Stone Game IX Array, Math, Greedy
Minimum Operations to Make Median of Array Equal to K Array, Greedy, Sorting
Destroy Sequential Targets Array, Hash Table, Counting
Smallest Missing Non-negative Integer After Operations Array, Hash Table, Math
Separate Black and White Balls String, Greedy, Two Pointers
Find the Maximum Number of Marked Indices Array, Two Pointers, Greedy
Maximum Split of Positive Even Integers Math, Greedy
Count Collisions on a Road String, Stack, Simulation
Video Stitching Array, Greedy, Dynamic Programming
Eliminate Maximum Number of Monsters Array, Greedy, Sorting
Minimum Number of Operations to Move All Balls to Each Box Array, String, Prefix Sum
Minimum Number of Arrows to Burst Balloons Array, Greedy, Sorting
Maximum Number of Removable Characters Array, String, Binary Search
Divide Chocolate Array, Binary Search, Greedy
Successful Pairs of Spells and Potions Array, Binary Search, Sorting
Search a 2D Matrix II Array, Matrix, Binary Search
Find Right Interval Array, Binary Search, Sorting
House Robber IV Array, Binary Search, Greedy
Minimize the Maximum Difference of Pairs Array, Binary Search, Greedy
Maximum Candies Allocated to K Children Array, Binary Search
H-Index II Array, Binary Search
Find the Smallest Divisor Given a Threshold Array, Binary Search
Maximum Value at a Given Index in a Bounded Array Binary Search, Greedy, Math
Find the Student That Will Replace the Chalk Array, Binary Search, Prefix Sum
Minimum Limit of Balls in a Bag Array, Binary Search
Magnetic Force Between Two Balls Array, Binary Search, Sorting
Minimum Number of Days to Make m Bouquets Array, Binary Search
Capacity to Ship Packages Within D Days Array, Binary Search
Find Minimum in Rotated Sorted Array II Array, Binary Search
Search in Rotated Sorted Array II Array, Binary Search
Minimum Swaps to Group All 1's Together II Array, Sliding Window
Length of Longest Subarray With at Most K Frequency Array, Hash Table, Sliding Window
Maximum Beauty of an Array After Applying Operation Array, Sliding Window, Sorting
Number of Subarrays with Bounded Maximum Array, Sliding Window, Two Pointers
Count the Number of Good Subarrays Array, Hash Table, Sliding Window
Swap For Longest Repeated Character Substring String, Sliding Window, Hash Table
Replace the Substring for Balanced String String, Sliding Window, Two Pointers
Get Equal Substrings Within Budget String, Sliding Window, Binary Search
Maximize the Confusion of an Exam String, Sliding Window, Prefix Sum
Frequency of the Most Frequent Element Array, Sliding Window, Greedy
Maximum Points You Can Obtain from Cards Array, Sliding Window, Prefix Sum
Grumpy Bookstore Owner Array, Sliding Window
Number of Substrings Containing All Three Characters String, Hash Table, Sliding Window
Longest Substring with At Most K Distinct Characters String, Hash Table, Sliding Window
Longest Substring with At Most Two Distinct Characters String, Hash Table, Sliding Window
Watering Plants II Array, Two Pointers, Simulation
Number of Subsequences That Satisfy the Given Sum Condition Array, Two Pointers, Sorting
3Sum With Multiplicity Array, Hash Table, Two Pointers
Most Profit Assigning Work Array, Two Pointers, Greedy
Push Dominoes String, Two Pointers, Dynamic Programming
Longest Mountain in Array Array, Two Pointers, Dynamic Programming
Partition Array Such That Maximum Difference Is K Array, Greedy, Sorting
Sort Transformed Array Array, Two Pointers, Math
Bag of Tokens Array, Two Pointers, Greedy
Max Number of K-Sum Pairs Array, Two Pointers, Hash Table
4Sum Array, Two Pointers, Sorting
Maximum Distance Between a Pair of Values Array, Two Pointers, Binary Search
Sum of Square Numbers Math, Two Pointers, Binary Search
Maximum OR Bit Manipulation, Array, Greedy
Minimum Array End Bit Manipulation, Greedy
Number of Wonderful Substrings Bit Manipulation, Hash Table, String
Bitwise ORs of Subarrays Bit Manipulation, Array, Dynamic Programming
Find the Longest Substring Containing Vowels in Even Counts Bit Manipulation, Hash Table, String
Longest Nice Subarray Bit Manipulation, Array, Sliding Window
UTF-8 Validation Bit Manipulation, Array
Maximum XOR for Each Query Bit Manipulation, Array, Prefix Sum
Count Number of Maximum Bitwise-OR Subsets Bit Manipulation, Backtracking, Enumeration
XOR Queries of a Subarray Bit Manipulation, Array, Prefix Sum
Decode XORed Permutation Bit Manipulation, Array, Brainteaser
Minimize XOR Bit Manipulation, Greedy
Flip String to Monotone Increasing String, Dynamic Programming, Bit Manipulation
Find the Xor-Beauty of Array Bit Manipulation, Array, Math
Maximum XOR After Operations Bit Manipulation, Array, Brainteaser
Longest Subarray With Maximum Bitwise AND Bit Manipulation, Array, Brainteaser
Minimum Number of Operations to Make Array XOR Equal to K Bit Manipulation, Array
Find The Original Array of Prefix Xor Bit Manipulation, Array, Prefix Sum
Bitwise XOR of All Pairings Bit Manipulation, Array, Brainteaser
Minimum Time to Repair Cars Array, Binary Search, Greedy
Maximum Value of an Ordered Triplet I Array, Math, Prefix Sum
Super Ugly Number Dynamic Programming, Math, Heap
Minimum Moves to Reach Target Score Math, Greedy
Integer Replacement Bit Manipulation, Greedy, Dynamic Programming
Reordered Power of 2 Math, Counting, Enumeration
Minimum Operations to Reduce an Integer to 0 Bit Manipulation, Greedy, Dynamic Programming
Maximum Product After K Increments Array, Greedy, Heap
Prime Subtraction Operation Array, Math, Greedy
Minimum Number of Operations to Make Array Empty Hash Table, Greedy, Counting
Number of Zero-Filled Subarrays Array, Math, Counting
4Sum II Hash Table, Array, Counting
Find Players With Zero or One Losses Hash Table, Array, Sorting
Minimum Area Rectangle Hash Table, Array, Geometry
Number of Boomerangs Hash Table, Math, Array
Group the People Given the Group Size They Belong To Hash Table, Array, Greedy
Optimal Partition of String Hash Table, String, Greedy
Count Number of Bad Pairs Hash Table, Array, Counting
Determine if Two Strings Are Close Hash Table, String, Counting
Brick Wall Hash Table, Array, Counting
Smallest String With Swaps Union Find, Hash Table, String
Number of Pairs of Interchangeable Rectangles Array, Hash Table, Math
Count Nice Pairs in an Array Array, Hash Table, Math
Longest Well-Performing Interval Array, Hash Table, Prefix Sum
Subarray Sums Divisible by K Array, Hash Table, Prefix Sum
Maximum Number of Integers to Choose From a Range I Hash Table, Greedy, Binary Search
Short Encoding of Words String, Trie, Hash Table
Replace Words String, Trie, Hash Table
Longest Word in Dictionary String, Trie, Hash Table
Word Subsets String, Hash Table, Counting
Number of Good Ways to Split a String String, Hash Table, Prefix Sum
Can Convert String in K Moves String, Hash Table, Greedy
Longest Substring With At Least K Repeating Characters String, Sliding Window, Divide and Conquer
Maximum Number of Occurrences of a Substring String, Sliding Window, Hash Table
Number of Ways to Split a String String, Math, Counting
Minimum Number of Frogs Croaking String, Greedy, Counting
Count Substrings That Differ by One Character String, Dynamic Programming
Maximum Length of a Concatenated String With Unique Characters String, Bit Manipulation, Backtracking
Count Words Obtained After Adding a Letter String, Bit Manipulation, Hash Table
Longest Word in Dictionary Through Deleting String, Two Pointers, Sorting
Number of Matching Subsequences String, Two Pointers, Binary Search
Find and Replace Pattern String, Hash Table
Count Number of Teams Array, Dynamic Programming
Uncrossed Lines Array, Dynamic Programming
Minimum ASCII Delete Sum for Two Strings String, Dynamic Programming
Unique Binary Search Trees Dynamic Programming, Math
Domino and Tromino Tiling Dynamic Programming
Paint Fence Dynamic Programming
Reach a Number Math, Binary Search
Check if Number is a Sum of Powers of Three Math, Number Theory
Number of Steps to Reduce a Number in Binary Representation to One String, Bit Manipulation, Simulation
Find Original Array From Doubled Array Array, Greedy, Sorting
Non-decreasing Array Array, Greedy
Minimum Moves to Equal Array Elements II Array, Math, Sorting
Word Search Array, String, Backtracking
Pacific Atlantic Water Flow Array, Depth-First Search, Breadth-First Search
Snakes and Ladders Array, Breadth-First Search, Matrix
Minimum Genetic Mutation Hash Table, String, Breadth-First Search
Jump Game III Array, Depth-First Search, Breadth-First Search
Count Unreachable Pairs of Nodes in an Undirected Graph Depth-First Search, Breadth-First Search, Union Find
Maximum Total Importance of Roads Graph, Greedy, Sorting
Find Closest Node to Given Two Nodes Depth-First Search, Graph
Maximal Network Rank Graph
Path With Minimum Effort Array, Binary Search, Depth-First Search
Time Needed to Inform All Employees Tree, Depth-First Search, Breadth-First Search
Reorder Routes to Make All Paths Lead to the City Zero Depth-First Search, Breadth-First Search, Graph
Possible Bipartition Depth-First Search, Breadth-First Search, Union Find
Minimum Height Trees Depth-First Search, Breadth-First Search, Graph
Detect Cycles in 2D Grid Array, Depth-First Search, Breadth-First Search
Number of Distinct Islands Array, Hash Table, Depth-First Search
Shortest Bridge Array, Depth-First Search, Breadth-First Search
The Earliest Moment When Everyone Become Friends Array, Union Find, Sorting
Number of Operations to Make Network Connected Depth-First Search, Breadth-First Search, Union Find
Count Sub Islands Array, Depth-First Search, Breadth-First Search
As Far from Land as Possible Array, Dynamic Programming, Breadth-First Search
Shortest Path in Binary Matrix Array, Breadth-First Search, Matrix
Number of Enclaves Array, Depth-First Search, Breadth-First Search
Minimum Number of Vertices to Reach All Nodes Graph
Find Eventual Safe States Depth-First Search, Breadth-First Search, Graph
All Paths From Source to Target Backtracking, Depth-First Search, Breadth-First Search
Keys and Rooms Depth-First Search, Breadth-First Search, Graph
Is Graph Bipartite? Depth-First Search, Breadth-First Search, Union Find
Graph Valid Tree Depth-First Search, Breadth-First Search, Union Find
Number of Connected Components in an Undirected Graph Depth-First Search, Breadth-First Search, Union Find
Rotate Function Array, Math, Dynamic Programming
Nth Digit Math, Binary Search
Bulb Switcher Math, Brainteaser
Count Triplets That Can Form Two Arrays of Equal XOR Array, Hash Table, Math
Concatenation of Consecutive Binary Numbers Math, Bit Manipulation, Simulation
Maximum Product of Word Lengths Array, String, Bit Manipulation
Sort Integers by The Power Value Dynamic Programming, Memoization, Sorting
Minimum Flips to Make a OR b Equal to c Bit Manipulation
Gray Code Math, Backtracking, Bit Manipulation
Maximum XOR of Two Numbers in an Array Array, Hash Table, Bit Manipulation
Bitwise AND of Numbers Range Bit Manipulation
Total Hamming Distance Array, Math, Bit Manipulation
Single Number III Array, Bit Manipulation
Single Number II Array, Bit Manipulation
Minimum Insertions to Balance a Parentheses String String, Stack, Greedy
Remove All Adjacent Duplicates in String II String, Stack
The Number of Weak Characters in the Game Array, Greedy, Sorting
Maximum Score From Removing Substrings String, Stack, Greedy
Minimum Number of Swaps to Make the String Balanced String, Stack, Greedy
Max Chunks To Make Sorted Array, Stack, Greedy
Sum of Subarray Ranges Array, Stack, Monotonic Stack
Reveal Cards In Increasing Order Array, Queue, Sorting
Reverse Substrings Between Each Pair of Parentheses String, Stack
Basic Calculator II Math, String, Stack
Validate Stack Sequences Array, Stack, Simulation
Next Greater Element III Math, Two Pointers, String
Maximum Width Ramp Array, Stack, Monotonic Stack
132 Pattern Array, Binary Search, Stack
Sum of Subarray Minimums Array, Dynamic Programming, Stack
Check If Word Is Valid After Substitutions String, Stack
Score of Parentheses String, Stack
Minimum Remove to Make Valid Parentheses String, Stack
Minimum Add to Make Parentheses Valid String, Stack, Greedy
Find K Closest Elements Array, Two Pointers, Binary Search
Kth Smallest Element in a Sorted Matrix Array, Binary Search, Sorting
Top K Frequent Words Array, Hash Table, String
K Closest Points to Origin Array, Math, Divide and Conquer
Partition Array into Disjoint Intervals Array, Greedy
Remove Duplicate Letters String, Stack, Greedy
Monotone Increasing Digits Math, Greedy
Maximum Swap Math, Greedy
Valid Triangle Number Array, Two Pointers, Binary Search
Remove Covered Intervals Array, Greedy, Sorting
Minimum Deletions to Make Character Frequencies Unique String, Hash Table, Greedy
Queue Reconstruction by Height Array, Greedy, Sorting
Two City Scheduling Array, Greedy, Sorting
Knight Dialer Dynamic Programming
2 Keys Keyboard Math, Dynamic Programming
Maximum Length of Pair Chain Array, Dynamic Programming, Greedy
Longest Turbulent Subarray Array, Dynamic Programming, Sliding Window
Number of Dice Rolls With Target Sum Dynamic Programming
Best Sightseeing Pair Array, Dynamic Programming
Maximum Sum Circular Subarray Array, Divide and Conquer, Dynamic Programming
Minimum Cost For Tickets Array, Dynamic Programming
Longest String Chain Array, Hash Table, Two Pointers
Combination Sum IV Array, Dynamic Programming
Ones and Zeroes Array, String, Dynamic Programming
Last Stone Weight II Array, Dynamic Programming
Stone Game Array, Math, Dynamic Programming
Count Numbers with Unique Digits Math, Dynamic Programming, Backtracking
Integer Break Math, Dynamic Programming
Perfect Squares Math, Dynamic Programming, Breadth-First Search
Triangle Array, Dynamic Programming
Minimum Falling Path Sum Array, Dynamic Programming, Matrix
Interleaving String String, Dynamic Programming
Delete Operation for Two Strings String, Dynamic Programming
Wiggle Subsequence Array, Dynamic Programming, Greedy
Number of Longest Increasing Subsequence Array, Dynamic Programming, Binary Indexed Tree
Longest Arithmetic Subsequence of Given Difference Array, Hash Table, Dynamic Programming
Maximum Length of Repeated Subarray Array, Binary Search, Dynamic Programming
Best Time to Buy and Sell Stock with Transaction Fee Array, Dynamic Programming, Greedy
Best Time to Buy and Sell Stock with Cooldown Array, Dynamic Programming
Delete and Earn Array, Hash Table, Dynamic Programming
Valid Sudoku Array, Hash Table, Matrix
Number of Closed Islands Array, Depth-First Search, Breadth-First Search
Surrounded Regions Array, Depth-First Search, Breadth-First Search
Game of Life Array, Matrix, Simulation
Count Square Submatrices with All Ones Array, Dynamic Programming, Matrix
Maximal Square Array, Dynamic Programming, Matrix
Unique Paths II Array, Dynamic Programming, Matrix
Minimum Path Sum Array, Dynamic Programming, Matrix
Sort the Matrix Diagonally Array, Sorting, Matrix
Max Increase to Keep City Skyline Array, Greedy, Matrix
Diagonal Traverse Array, Matrix, Simulation
Count Number of Nice Subarrays Array, Hash Table, Math
Binary Subarrays With Sum Array, Hash Table, Sliding Window
Maximum Erasure Value Array, Hash Table, Sliding Window
Minimum Operations to Reduce X to Zero Array, Hash Table, Binary Search
Longest Subarray of 1's After Deleting One Element Array, Dynamic Programming, Sliding Window
Continuous Subarray Sum Array, Hash Table, Math
Contiguous Array Array, Hash Table, Prefix Sum
Subarray Product Less Than K Array, Sliding Window, Binary Search
Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold Array, Sliding Window
Maximum Number of Vowels in a Substring of Given Length String, Sliding Window
Valid Parenthesis String String, Dynamic Programming, Stack
String Compression Two Pointers, String
Count and Say String, Simulation
Majority Element II Array, Hash Table, Sorting
Increasing Triplet Subsequence Array, Greedy
H-Index Array, Sorting, Counting Sort
Shortest Unsorted Continuous Subarray Array, Two Pointers, Sorting
Next Permutation Array, Two Pointers
Find All Duplicates in an Array Array, Hash Table
Factorial Trailing Zeroes Math
Count Primes Math, Sieve of Eratosthenes

Hard (139)

Count Ways to Make Array With Product Array, Math, Dynamic Programming
Count the Number of Ideal Arrays Math, Dynamic Programming, Combinatorics
Number of Ways to Rearrange Sticks With K Sticks Visible Math, Dynamic Programming, Combinatorics
The Number of Good Subsets Array, Math, Dynamic Programming
Number of Ways to Reorder Array to Get Same BST Array, Math, Divide and Conquer
Make Array Strictly Increasing Array, Binary Search, Dynamic Programming
Odd Even Jump Array, Dynamic Programming, Stack
Maximum Number of Events That Can Be Attended II Array, Binary Search, Dynamic Programming
Minimum Replacements to Sort the Array Array, Math, Greedy
Create Sorted Array Through Instructions Array, Binary Search, Divide and Conquer
Painting the Walls Array, Dynamic Programming
Reverse Pairs Array, Binary Search, Divide and Conquer
Number of Ways to Separate Numbers String, Dynamic Programming, Suffix Array
Painting a Grid With Three Different Colors Dynamic Programming, Bitmask
Minimum Incompatibility Array, Dynamic Programming, Bit Manipulation
Number of Distinct Roll Sequences Dynamic Programming, Memoization
Form Largest Integer With Digits That Add up to Target Array, String, Dynamic Programming
Build Array Where You Can Find The Maximum Exactly K Comparisons Dynamic Programming, Prefix Sum
Stone Game VIII Array, Math, Dynamic Programming
Allocate Mailboxes Array, Math, Dynamic Programming
Constrained Subsequence Sum Array, Dynamic Programming, Queue
Restore the Array String, Dynamic Programming
Count All Valid Pickup and Delivery Options Math, Dynamic Programming, Combinatorics
Maximum Height by Stacking Cuboids Array, Dynamic Programming, Sorting
Cherry Pickup II Array, Dynamic Programming, Matrix
Strange Printer String, Dynamic Programming
Number of Ways to Stay in the Same Place After Some Steps Dynamic Programming
Maximum Value of K Coins From Piles Array, Dynamic Programming, Prefix Sum
Count Special Integers Math, Dynamic Programming, Combinatorics
Number of Great Partitions Array, Dynamic Programming
Minimum Cost to Split an Array Array, Hash Table, Dynamic Programming
Paths in Matrix Whose Sum Is Divisible by K Array, Dynamic Programming, Matrix
Special Binary String String, Recursion, Divide and Conquer
Count Different Palindromic Subsequences String, Dynamic Programming
Smallest K-Length Subsequence With Occurrences of a Letter String, Stack, Greedy
Valid Palindrome III String, Dynamic Programming
Count Anagrams Hash Table, Math, String
String Compression II String, Dynamic Programming
Apply Operations to Maximize Score Array, Math, Stack
Meeting Rooms III Array, Sorting, Simulation
Smallest Range Covering Elements from K Lists Array, Hash Table, Greedy
Minimize Deviation in Array Array, Greedy, Heap (Priority Queue)
Maximum Performance of a Team Array, Greedy, Sorting
Construct Target Array With Multiple Sums Array, Heap (Priority Queue), Math
Minimum Number of Operations to Make Array Continuous Array, Hash Table, Binary Search
Put Marbles in Bags Array, Greedy, Sorting
Minimum Time to Visit a Cell In a Grid Array, Matrix, Graph
Minimum Number of Days to Disconnect Island Array, Matrix, Depth-First Search
Number of Increasing Paths in a Grid Array, Matrix, Dynamic Programming
Checking Existence of Edge Length Limited Paths Array, Union Find, Graph
Find All People With Secret Graph, Union Find, Depth-First Search
Minimum Obstacle Removal to Reach Corner Array, Matrix, Graph
Number of Good Paths Array, Tree, Graph
Largest Component Size by Common Factor Array, Math, Union Find
Critical Connections in a Network Graph, Depth-First Search, Biconnected Component
Bus Routes Array, Hash Table, Breadth-First Search
Number of Restricted Paths From First to Last Node Graph, Dynamic Programming, Shortest Path
Sliding Puzzle Array, Matrix, Breadth-First Search
Jump Game IV Array, Hash Table, Breadth-First Search
Trapping Rain Water II Array, Matrix, Heap (Priority Queue)
Escape the Spreading Fire Array, Matrix, Binary Search
Grid Illumination Array, Hash Table, Matrix
Shortest Distance from All Buildings Array, Matrix, Breadth-First Search
Minimum Moves to Spread Stones Over Grid Array, Matrix, Dynamic Programming
Making A Large Island Array, Matrix, Depth-First Search
Unique Paths III Array, Matrix, Backtracking
Number of Submatrices That Sum to Target Array, Matrix, Hash Table
Longest Increasing Path in a Matrix Array, Matrix, Dynamic Programming
Maximal Rectangle Array, Matrix, Stack
Minimum Difficulty of a Job Schedule Array, Dynamic Programming
Minimum Cost to Cut a Stick Array, Dynamic Programming, Sorting
Minimum White Tiles After Covering With Carpets String, Dynamic Programming, Prefix Sum
Maximum Number of Groups With Increasing Length Array, Greedy, Sorting
Number of Ways to Earn Points Array, Dynamic Programming
Scramble String String, Dynamic Programming
Number of Music Playlists Math, Dynamic Programming, Combinatorics
Profitable Schemes Array, Dynamic Programming
Distinct Subsequences II String, Dynamic Programming
Cherry Pickup Array, Matrix, Dynamic Programming
Number of Ways to Paint N × 3 Grid Dynamic Programming
Tallest Billboard Array, Dynamic Programming
Best Time to Buy and Sell Stock IV Array, Dynamic Programming
Burst Balloons Array, Dynamic Programming
Frog Jump Array, Hash Table, Dynamic Programming
Minimum Falling Path Sum II Array, Matrix, Dynamic Programming
Dungeon Game Array, Matrix, Dynamic Programming
Minimum Time to Complete All Tasks Array, Greedy, Sorting
Minimum Number of Refueling Stops Array, Greedy, Dynamic Programming
IPO Array, Greedy, Sorting
Minimum Number of Taps to Open to Water a Garden Array, Greedy, Dynamic Programming
Maximum Number of Tasks You Can Assign Array, Binary Search, Greedy
Find the Kth Smallest Sum of a Matrix With Sorted Rows Array, Matrix, Binary Search
Russian Doll Envelopes Array, Binary Search, Dynamic Programming
Maximum Running Time of N Computers Array, Binary Search, Greedy
Minimum Time to Complete Trips Array, Binary Search
Kth Smallest Number in Multiplication Table Math, Binary Search
Split Array Largest Sum Array, Binary Search, Greedy
Minimum Number of Flips to Make the Binary String Alternating String, Sliding Window, Dynamic Programming
Take K of Each Character From Left and Right String, Hash Table, Sliding Window
Minimum Number of K Consecutive Bit Flips Array, Sliding Window, Prefix Sum
Shortest Subarray with Sum at Least K Array, Prefix Sum, Sliding Window
Count Subarrays With Fixed Bounds Array, Sliding Window, Two Pointers
Maximum Number of Robots Within Budget Array, Sliding Window, Two Pointers
Minimum Window Subsequence String, Two Pointers, Dynamic Programming
Minimum Number of Moves to Make Palindrome String, Two Pointers, Greedy
Find K-th Smallest Pair Distance Array, Two Pointers, Binary Search
Subarrays with K Different Integers Array, Hash Table, Sliding Window
Shortest Path Visiting All Nodes Bit Manipulation, Breadth-First Search, Graph
Count the Number of Square-Free Subsets Bit Manipulation, Dynamic Programming, Bitmask
Maximum AND Sum of Array Bit Manipulation, Dynamic Programming, Bitmask
Find Subarray With Bitwise OR Closest to K Bit Manipulation, Array, Binary Search
Minimum One Bit Operations to Make Integers Zero Bit Manipulation, Math, Dynamic Programming
Smallest Good Base Math, Binary Search, Number Theory
Number of Digit One Math, Digit DP, Recursion
Preimage Size of Factorial Zeroes Function Math, Binary Search, Number Theory
Nth Magical Number Math, Binary Search, Number Theory
Largest Multiple of Three Array, Greedy, Dynamic Programming
Count of Range Sum Fenwick Tree, Divide and Conquer, Prefix Sum
Substring with Concatenation of All Words Hash Table, String, Sliding Window
Max Points on a Line Hash Table, Math, Geometry
Longest Happy Prefix String, KMP, Rolling Hash
Count Unique Characters of All Substrings of a Given String String, Hash Table, Counting
Shortest Palindrome String, KMP, Rolling Hash
Max Value of Equation Array, Monotonic Queue, Sliding Window
Count of Smaller Numbers After Self Array, Fenwick Tree, Divide and Conquer
Stone Game IV Math, Dynamic Programming, Game Theory
Stone Game III Array, Dynamic Programming, Game Theory
Palindrome Partitioning II String, Dynamic Programming
Wildcard Matching String, Dynamic Programming, Greedy
Distinct Subsequences String, Dynamic Programming
Max Dot Product Between Two Subsequences Array, Dynamic Programming
Minimum Insertion Steps to Make a String Palindrome String, Dynamic Programming
Swim in Rising Water Array, Binary Search, Depth-First Search
Word Ladder Hash Table, String, Breadth-First Search
Longest Cycle in a Graph Depth-First Search, Graph, Topological Sort
Number of Visible People in a Queue Array, Stack, Monotonic Stack
Longest Valid Parentheses String, Dynamic Programming, Stack
Count Vowels Permutation Dynamic Programming
Best Time to Buy and Sell Stock III Array, Dynamic Programming

Topics Google asks most

Arrays 372 problems
Dynamic Programming 155 problems
Strings 150 problems
Hash Table 109 problems
Greedy 108 problems
Math 105 problems
Sorting 92 problems
Matrix 72 problems
Binary Search 71 problems
Breadth-First Search 57 problems
Bit Manipulation 55 problems
Two Pointers 52 problems