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

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

一刷
題解：two pointer

public class Solution {
    public String reverseString(String s) {
        char[] chs = s.toCharArray();
        int l = 0, r = s.length()-1;
        while(l<r){
            char temp = chs[l];
            chs[l] = chs[r];
            chs[r] = temp;
            l++;
            r--;
        }
        return new String(chs);
    }
}