Length of Last Word

Description

Length of Last Word - LeetCode

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

A word is a maximal substring¹ consisting of non-space characters only.

Examples

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

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

Code

class Solution {
public:
    int lengthOfLastWord(string s) {
        int end = s.length() - 1;
 
        while(end >= 0 && s[end] == ' '){
            end--;
        }
 
        int start = end;
 
        while(start >= 0 && s[start] != ' '){
            start--;
        }
 
        return end - start;
    }
};

Approach

IMPORTANT

Need to watchout for Trailing Whitespaces

1. Create the end pointer to point at the last character in the string
2. Traverse the pointer backward until the end pointer is pointing to a non-whitespace
3. Create the start pointer to point at the last character of the last word (where end pointer is pointing at)
4. Traverse the start pointer until pointing at a whitespace or start of the string
5. return the end index - start index

Footnotes

1. A substring is a contiguous non-empty sequence of characters within a string. ↩