题意：

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

Example:

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

就是将一个字符串翻转输出。

public String reverseString(String s) {        if(s == null || s.length() < 2)            return s;        char[] chars = s.toCharArray();        for(int i=0; i