题目：

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

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

思路：

• 题意：反转字符串
• 不用考虑为空的情况，这种情况sb.toString()也是null，倒叙遍历，StringBuffer相加

代码：

public class Solution {
    public String reverseString(String s) {
        StringBuffer sb = new StringBuffer();
        int n = s.length();
        for(int i = n-1;i >= 0;i--){
            sb.append(s.charAt(i));
        }
        return sb.toString();
    }
}