输入: "hello"
输出: "olleh"

输入: "A man, a plan, a canal: Panama"
输出: "amanaP :lanac a ,nalp a ,nam A"

class Solution {
    public String reverseString(String s) {
        if(s==null||s.length()==1){
            return s;
        }
        char[] chars=s.toCharArray();//将字符串对象中的字符转换为一个字符数组
        int length=s.length();
        for(int i=0;i<length/2;i++){
            char temp=chars[i];
            chars[i]=chars[length-1-i];
            chars[length-1-i]=temp;
        }
        //return chars; //报错 char[] cannot be converted to String
        return String.valueOf(chars);//把参数中的值，转为String类型输出
    }
}