Problem URL: Reverse words in a string II

We will reverse the entire string, then reverse each word. We will use two pointers to keep track of the start and end of each word.

class Solution:
    def reverseWords(self, s: List[str]) -> None:
        self.reverse(s, 0, len(s)-1)
        self.reverseEachWord(s)

    def reverseEachWord(self, l: List[str]) -> None:
        n = len(l)
        start, end = 0, 0
        while start < n:
            while end < n and l[end] != ' ':
                end += 1

            self.reverse(l, start, end-1)

            start = end+1
            end += 1

    def reverse(self, l: List[str], left: int, right: int) -> None:
        while left < right:
            l[left], l[right] = l[right], l[left]
            left += 1
            right -= 1

Time complexity: O(n), n is the length of the string
Space complexity: O(1)