This question is very simple, is the basic version, the time complexity of the double pointer problem is O (N), the spatial complexity is O (1)
class Solution: def reverseString(self, s: List[str]) -> None: """ Do not return anything, modify s in-place instead. """ if s is None or len(s) <= 1: return s start, end = 0, len(s) - 1 while start < end: s[start], s[end] = s[end], s[start] start += 1 end -=1