58. Length of Last Word

Problem

Given a string s consisting of some words separated by some number of 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 <= 104
• s consists of only English letters and spaces ' '.
• There will be at least one word in s.

Problem Summary

Given a string s consisting of several words, with some space characters separating the words before and after. Return the length of the last word in the string. A word refers to a maximal substring consisting only of letters and containing no space characters.

Solution Approach

• First filter out spaces from the end to find the end of the word, then traverse backward from the end to find the beginning of the word. Finally, subtract the two positions to get the length of the word.

Code

package leetcode

func lengthOfLastWord(s string) int {
	last := len(s) - 1
	for last >= 0 && s[last] == ' ' {
		last--
	}
	if last < 0 {
		return 0
	}
	first := last
	for first >= 0 && s[first] != ' ' {
		first--
	}
	return last - first
}