Length of Last Word

Easy
215.

Length of Last Word

EasyStringAmazonMicrosoftTCSInfosysAccenture

Length of Last Word is an easy coding problem on strings, asked in Amazon, Microsoft, TCS and Infosys interviews.

Given a string s consisting of words and spaces, return the length of the last word.

A word is a maximal run of non-space characters.

Example 1

Input
s = "Hello World"
Output
5

Example 2

Input
s = " fly me to the moon "
Output
4
Explanation
The last word is moon, and the trailing spaces are ignored.

Example 3

Input
s = "a"
Output
1

Constraints

  • 1 <= s.length <= 60
  • s consists of English letters and spaces.
  • There is at least one word in s.
Write your solution here. Running it against the tests needs a free account — what you type comes with you.Sign in to run
/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLastWord = function(s) {
    // Write your code here
    
};

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Length of Last Word — Solution in Python, Java & C++

Length of Last Word solution explained: step-by-step approach, complexity and code in Python, Java, C++ and JavaScript. An easy problem on strings.

Length of Last Word is an easy coding problem on strings, asked in Amazon, Microsoft, TCS and Infosys interviews.

  • Difficulty: Easy
  • Topics: Strings
  • Asked at: Amazon, Microsoft, TCS, Infosys, Accenture
  • 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 a string s consisting of words and spaces, return the length of the last word.

A word is a maximal run of non-space characters.

Example 1

Input: s = "Hello World"
Output: 5

Example 2

Input: s = "   fly me   to   the moon  "
Output: 4
Explanation: The last word is moon, and the trailing spaces are ignored.

Example 3

Input: s = "a"
Output: 1

Constraints

  • 1 <= s.length <= 60
  • s consists of English letters and spaces.
  • There is at least one word in s.

Hints for Length of Last Word

  1. Hint 1

    Work from the right rather than splitting the whole string.

  2. Hint 2

    First skip any trailing spaces, then count characters until the next space or the start of the string.

How to solve Length of Last Word

Scan from the right: skip trailing spaces, then count characters until the next space or the start.

Approach

  1. Set i to the last index and move left while s[i] is a space.
  2. Count characters while i >= 0 and s[i] is not a space.
  3. Return the count.

Why it works

The last word is the final run of non-space characters, and walking backwards reaches it without touching the rest of the string.

Complexity

  • Time — O(n) worst case, typically O(length of last word)
  • Space — O(1)

Pitfalls

  • Trailing spaces are the trap — "hello " has a last word of length 5.
  • split() and taking the last piece works but allocates every word.

Reference solution

Python

def lengthOfLastWord(s: str) -> int:
    i = len(s) - 1
    while i >= 0 and s[i] == " ":
        i -= 1
    length = 0
    while i >= 0 and s[i] != " ":
        length += 1
        i -= 1
    return length

Java

public static int lengthOfLastWord(String s) {
    int i = s.length() - 1;
    while (i >= 0 && s.charAt(i) == ' ') i--;
    int len = 0;
    while (i >= 0 && s.charAt(i) != ' ') {
        len++;
        i--;
    }
    return len;
}

C++

int lengthOfLastWord(string s) {
    int i = (int) s.size() - 1;
    while (i >= 0 && s[i] == ' ') i--;
    int len = 0;
    while (i >= 0 && s[i] != ' ') {
        len++;
        i--;
    }
    return len;
}

JavaScript

var lengthOfLastWord = function(s) {
    let i = s.length - 1;
    while (i >= 0 && s[i] === " ") i--;
    let len = 0;
    while (i >= 0 && s[i] !== " ") {
        len++;
        i--;
    }
    return len;
};

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

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