Problem

Solution 1

Intuition

This problem requires finding the last word and finding its length. We can use Python in order to efficiently manipulate the string to find the last word.

Approach

The first approach is to use in-built python functions to strip the trailing spaces, split the words by the space character, and then find the length of the last word in the list.

Complexity

• Time complexity: $O(n)$ time complexity as the entire string is manipulated.
• Space complexity: $O(n)$ as Python creates a list after the call to split which is used for finding the last word. Even though this is not saved as a variable, it will take space in the stack.

Code

class Solution:
    def lengthOfLastWord(self, s: str) -> int:
        return len(s.strip().split(' ')[-1])

Solution 2

Intuition

We can use a two pointer approach in order to find the start and end of the last word for an easy scanning approach.

Approach

The second approach is to decrement a pointer from the end until the last letter of the last word is reached, and then continue counting the length until a space character is reached.

Complexity

• Time complexity: $O(n)$ as the iteration can take up the entire length of the string.
• Space complexity: $O(1)$ as no additional data structures are created.

Code

class Solution:
    def lengthOfLastWord(self, s: str) -> int:
        return len(s.strip().split(' ')[-1])

Approach 2 Code

class Solution:
    def lengthOfLastWord(self, s: str) -> int:
        P = len(s) - 1
        res = 0

        while P >= 0 and s[P] == ' ':
            P -= 1
        while P >= 0 and s[P] != ' ':
            P -= 1
            res += 1
        return res