23. Length of Last Word

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.

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

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

Input: s = "luffy is still joyboy"
Output: 6

Problem Breakdown:

1. Trim trailing spaces from the string so we can find the last word easily.

• s = s.rstrip()

2. Start from the end of the trimmed string and count characters until we hit a space or the beginning.

• length = 0
  for i in range(len(s) - 1, -1, -1):
      if s[i] == ' ':
          break
      length += 1

3. Return the count, which is the length of the last word.

• return length

Summary:

Strip trailing spaces, then count characters backwards from the end until hitting a space. Alternatively, use built-in split to get the last word directly.

Time and Space Complexity:

Time Complexity: O(n) - we may traverse the entire string.

Space Complexity: O(1) - only a counter variable used (or O(n) if using split).

Python Solution:

def lengthOfLastWord(s):
    s = s.rstrip()
    length = 0
    for i in range(len(s) - 1, -1, -1):
        if s[i] == ' ':
            break
        length += 1
    return length

JavaScript Solution:

var lengthOfLastWord = function(s) {
    s = s.trimEnd();
    let length = 0;
    for (let i = s.length - 1; i >= 0; i--) {
        if (s[i] === ' ') break;
        length++;
    }
    return length;
};

Java Solution:

class Solution {
    public int lengthOfLastWord(String s) {
        s = s.trim();
        int length = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            if (s.charAt(i) == ' ') break;
            length++;
        }
        return length;
    }
}