Reverse String

344. Reverse String

Difficulty: Easy

Related Topics: Two Pointers, String

Write a function that reverses a string. The input string is given as an array of characters s.

You must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Input: s = [“h”,”e”,”l”,”l”,”o”] Output: [“o”,”l”,”l”,”e”,”h”]

Example 2:

Input: s = [“H”,”a”,”n”,”n”,”a”,”h”] Output: [“h”,”a”,”n”,”n”,”a”,”H”]

Code:

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        left = 0
        right = len(s) -1
        while left < right:
            tmp = s[left]
            s[left] = s[right]
            s[right] = tmp
            left+=1
            right-=1

Feedbacks:

Since I need to use two pointers for this problem, I set ‘left’ as 0, ‘right’ as s.length-1. And while right is larger than left, I swap s[left] and s[right], and increase left by one while decrease right by one. And this will reverse the string correctly.