58. Length of Last Word

1. 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.

2. Example

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.

3. Constraints

• 1 <= s.length <= $10^4$
• s consists of only English letters and spaces ' ‘.
• There will be at least one word in s.

4. Solutions

Two Pointers

n = str.size()
Time complexity: O(n)
Space complexity: O(1)

class Solution {
public:
    int lengthOfLastWord(const string &str) {
        int right = str.size() - 1;
        while (str[right] == ' ') {
            --right;
        }
        int left = right;
        while (left >= 0 && str[left] != ' ') {
            --left;
        }

        return right - left;
    }
};