Leetcode: 344. Reverse String

Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "hello", return "olleh".

Code (Java):

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public class Solution {     public String reverseString(String s) {         if (s == null || s.length() == 0) {             return "";         }                   char[] cs = s.toCharArray();         int start = 0;         int end = s.length() - 1;                   while (start < end) {             swap(cs, start, end);             start++;             end--;         }                   return new String(cs);     }           private void swap(char[] cs, int i, int j) {         char temp = cs[i];         cs[i] = cs[j];         cs[j] = temp;     } }