Concatenation of Array

Easy
192.

Concatenation of Array

EasyArraySimulationAmazonTCS

Concatenation of Array is an easy coding problem on arrays and simulation, asked in Amazon and TCS interviews.

Given an integer array nums of length n, return an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for every 0 <= i < n.

In other words, ans is nums concatenated with itself.

Example 1

Input
nums = [1,2,1]
Output
[1,2,1,1,2,1]

Example 2

Input
nums = [1,3,2,1]
Output
[1,3,2,1,1,3,2,1]

Example 3

Input
nums = [7]
Output
[7,7]

Constraints

  • 1 <= nums.length <= 40
  • 1 <= nums[i] <= 1000
Write your solution here. Running it against the tests needs a free account — what you type comes with you.Sign in to run
/**
 * @param {number[]} nums
 * @return {number[]}
 */
var getConcatenation = function(nums) {
    // Write your code here
    
};

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Concatenation of Array — Solution in Python, Java & C++

Concatenation of Array solution explained: step-by-step approach, complexity and code in Python, Java, C++ and JavaScript. An easy problem.

Concatenation of Array is an easy coding problem on arrays and simulation, asked in Amazon and TCS interviews.

  • Difficulty: Easy
  • Topics: Arrays, Simulation
  • Asked at: Amazon, TCS
  • Time limit: 2 s
  • Memory limit: 256 MB
  • Languages: JavaScript, TypeScript, Python, Java, C++, C, C#, Go, Kotlin, Swift, Rust, PHP and Ruby

Problem statement

Given an integer array nums of length n, return an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for every 0 <= i < n.

In other words, ans is nums concatenated with itself.

Example 1

Input: nums = [1,2,1]
Output: [1,2,1,1,2,1]

Example 2

Input: nums = [1,3,2,1]
Output: [1,3,2,1,1,3,2,1]

Example 3

Input: nums = [7]
Output: [7,7]

Constraints

  • 1 <= nums.length <= 40
  • 1 <= nums[i] <= 1000

Hints for Concatenation of Array

  1. Hint 1

    Append the array to itself — either with a library concatenation or by looping over it twice.

How to solve Concatenation of Array

The answer is the array followed by itself.

Approach

  1. Return nums + nums (or loop over the input twice, appending).

Why it works

ans[i] = nums[i] and ans[i + n] = nums[i] is the definition of concatenation with itself.

Complexity

  • Time — O(n)
  • Space — O(n)

Pitfalls

  • Iterating with index i % n up to 2n is the same thing without a library call.

Reference solution

Python

def getConcatenation(nums):
    return list(nums) + list(nums)

Java

public static int[] getConcatenation(int[] nums) {
    int n = nums.length;
    int[] out = new int[2 * n];
    for (int i = 0; i < n; i++) {
        out[i] = nums[i];
        out[i + n] = nums[i];
    }
    return out;
}

C++

vector<int> getConcatenation(vector<int>& nums) {
    vector<int> out(nums);
    for (int x : nums) out.push_back(x);
    return out;
}

JavaScript

var getConcatenation = function(nums) {
    return nums.concat(nums);
};

Also on the editorial tab: C, C#, Go, Kotlin, PHP, Ruby, Rust, Swift, TypeScript.

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