Length of Last Word – Solution & Complexity

Q: What is the time and space complexity of Length of Last Word?

The optimal Length of Last Word solution runs in `O(n)` time and `O(1)` space. Scan from the end, skipping trailing spaces, then count the final word's characters.

Q: What is the most efficient way to solve Length of Last Word?

Scan from the end, skipping trailing spaces, then count the final word's characters. This gives `O(n)` time complexity, and is a classic strings problem.

Q: How do you solve Length of Last Word in Python & JavaScript?

We provide a worked Length of Last Word solution in Python & JavaScript with a step-by-step explanation above. You can also open the interactive editor to write and run your own Python solution against the test cases in the browser.

Q: Is Length of Last Word an easy or hard interview question?

Length of Last Word is generally rated **Easy**. It tests strings, which are common coding-interview patterns.

1. Understand What Counts as a Word

A word is any maximal run of non-space characters.
Leading, trailing, and repeated spaces should not count as part of a word.
If the string contains only spaces, the answer is 0.

2. Simple Split-Based Idea

One straightforward approach is to split the string on whitespace.
The last token is the last word, and its length is the answer.
This is easy to read, but it creates a list of all words.

def length_of_last_word(s):
    words = s.split()
    if not words:
        return 0
    return len(words[-1])

3. Scan from the End

The last word is closest to the end of the string.
First skip trailing spaces.
Then count characters until you reach another space or the beginning of the string.

i = len(s) - 1
while i >= 0 and s[i] == " ":
    i -= 1

4. Count the Last Word Characters

After trailing spaces are skipped, i points at the last character of the last word.
Move left while characters are not spaces, increasing a counter.
If there was no word, the counter stays at 0.

length = 0
while i >= 0 and s[i] != " ":
    length += 1
    i -= 1

5. Complete Solution and Complexity

The final solution uses the end scan to avoid storing extra words.
Time complexity is O(n) in the worst case.
Space complexity is O(1).

def length_of_last_word(s: str) -> int:
    i = len(s) - 1

    while i >= 0 and s[i] == " ":
        i -= 1

    length = 0
    while i >= 0 and s[i] != " ":
        length += 1
        i -= 1

    return length

Length of Last Word – Solution & Complexity

1. Understand What Counts as a Word

2. Simple Split-Based Idea

3. Scan from the End

4. Count the Last Word Characters

5. Complete Solution and Complexity

FAQ

What is the time and space complexity of Length of Last Word?

What is the most efficient way to solve Length of Last Word?

How do you solve Length of Last Word in Python & JavaScript?

Is Length of Last Word an easy or hard interview question?