反转字符串

import java.util.*;


public class Solution {
    /**
     * 反转字符串
     * @param str string字符串 
     * @return string字符串
     */
    public String solve (String str) {
        // write code here
        if(str == null) return null;

        char[] c = str.toCharArray();
        for(int i = 0, j = c.length - 1; i < j; ++i,--j){
            char temp = c[i];
            c[i] = c[j];
            c[j] = temp;
        }
        return new String(c);
    }
}