Length of Last Word

LeetCode 58 | Difficulty: Easy

Easy

Problem Description

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

A word is a maximal substring consisting of non-space characters only.

Example 1:

Input: s = "Hello World"
Output: 5
Explanation: The last word is "World" with length 5.

Example 2:

Input: s = "   fly me   to   the moon  "
Output: 4
Explanation: The last word is "moon" with length 4.

Example 3:

Input: s = "luffy is still joyboy"
Output: 6
Explanation: The last word is "joyboy" with length 6.

Constraints:

- `1 <= s.length <= 10^4`

- `s` consists of only English letters and spaces `' '`.

- There will be at least one word in `s`.

Topics: String

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Approach

String Processing

Consider character frequency counts, two-pointer approaches, or building strings efficiently. For pattern matching, think about KMP or rolling hash. For palindromes, expand from center or use DP.

When to use

Anagram detection, palindrome checking, string transformation, pattern matching.

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Solutions

Solution 1: C# (Best: 132 ms)

Metric	Value
Runtime	132 ms
Memory	N/A
Date	2017-10-22

Solution

public class Solution {
    public int LengthOfLastWord(string s) {
        if(string.IsNullOrEmpty(s) || s.Split(new char[] { ' '},StringSplitOptions.RemoveEmptyEntries).Count()==0)
        return 0;
        
        var result =  s.Split(new char[] { ' '}, StringSplitOptions.RemoveEmptyEntries).ToArray();
        return result[result.Length-1].Length;
    }
}

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Complexity Analysis

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

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Interview Tips

Key Points

• Start by clarifying edge cases: empty input, single element, all duplicates.