Reverse String
Updated Jan 31, 2026
Problem
Write a function that reverses a string.
The input string is given as a list of characters. You must do this by modifying the input list in-place with O(1) extra memory.
Constraints
1 <= s.length <= 10^5
s[i] is a printable ASCII character.
Examples
Example 1
Input:
s = ["h","e","l","l","o"]
Output:
["o","l","l","e","h"]
The string "hello" reversed is "olleh".
Example 2
Input:
s = ["H","a","n","n","a","h"]
Output:
["h","a","n","n","a","H"]
Function Signature
def reverseString(self, s: list[str]) -> None
How to Submit
Implement a Solution class with a reverseString method.
Your method will be called with the input parameters and should return the answer.