LeetCode 58: Length of Last Word

Meta Data

#

Difficulty: easy First Attempt: 2022-05-11

• Submissions: Accepted ×3 → Wrong Answer → Accepted ×3 → Runtime Error → Accepted ×3

Approach

#

s.split() drops leading and trailing spaces and merges runs of spaces, so its last element is the last word (String Template 6). Without splitting everything, scan from the end: skip spaces, then count non-spaces.

My Attempts

#

One 2022-05 version used split(" ")[-1], whose last element is empty when the string ends with a space: "a " returned 0 instead of 1. A 2022-08 rewrite put the -1 inside split(-1) (TypeError).

Solution

#

class Solution:
    def lengthOfLastWord(self, s: str) -> int:
        i = len(s) - 1
        while s[i] == " ":
            i -= 1
        n = 0
        while i >= 0 and s[i] != " ":
            n += 1
            i -= 1
        return n

Complexity

#

Time O(n), space O(1).

Mistakes to Avoid

#

• The string may end with spaces; split(" ")[-1] yields an empty string.

Interview Explanation

#

From the end I skip trailing spaces and count the following non-space characters, in O(1) space; taking the last element of split() also works.