README_EN.md

344. Reverse String

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Description

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

 

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"]

 

Constraints:

• 1 <= s.length <= 105
• s[i] is a printable ascii character.

 

Follow up: Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory.

Solutions

Python3

class Solution:
    def reverseString(self, s: List[str]) -> None:
        """
        Do not return anything, modify s in-place instead.
        """
        s[:] = s[::-1]

Java

class Solution {
    public void reverseString(char[] s) {
        int n;
        if (s == null || (n = s.length) < 2) return;
        int i = 0, j = n - 1;
        while (i < j) {
            char t = s[i];
            s[i] = s[j];
            s[j] = t;
            ++i;
            --j;
        }
    }
}

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