Leetcode 58: Length of Last Word

1. Problem Statement (Simple Explanation)

You’re given a string s that contains:

• English letters

• Spaces ' '

A word is defined as a maximal substring of non-space characters.

You must return the length of the last word in s.

There is guaranteed to be at least one word in the string.

2. Examples

Example 1:

Input: s = "Hello World"

Last word = "World" → length = 5.

Output: 5

Example 2:

Input: s = "   fly me   to   the moon  "

Last word = "moon" → length = 4.

Output: 4

Example 3:

Input: s = "luffy is still joyboy"

Last word = "joyboy" → length = 6.

Output: 6

3. Approach – Scan from the End (O(n), O(1))

We only need the last word, so we can efficiently scan from the end of the string:

1. Start from the last index and skip all trailing spaces.

2. Then, count characters until:

• We hit a space, or

• We reach the beginning of the string.

That count is the length of the last word.

Pseudo-code:

Complexity:

Let n = len(s):

• Time: O(n) in worst case (single pass from end).

• Space: O(1) extra.

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