s = "hello" => "olleh"
    
    /*
    * 思路1：反向遍历字符串
    */
    var s1 = "";
    for (var i = s.length-1; i >= 0; i--) {
        s1 += s[i];
    }
    return s1;
    /*
    * 思路2:1.建立两个指针，分别指向首尾，遍历数组，直至指针相遇；
            2.将两个指针值交换
            超出时间
    */
    //     var s1 = Array.from(s);
    //     var left = 0;
    //     var right = s.length-1;
    //     while (left < right) {
    //         temp = s1[left];
    //         s1[left] = s1[right];
    //         s1[right] = temp;
    //     }
    //     return s1.join("");

    var reverse = function(x) {
        var minn = -(1 << 30) * 2;
        var maxn = (1 << 30) * 2 - 1;
        var tag = x < 0 ? -1 : 1;
        var s = x * tag + '';
        var s1 = ''
        for (var i = s.length; i--;) {
            s1 += s[i];
        }
        var res = (s1 - 0) * tag;
        if (res < minn || res > maxn)
            return 0;
        else
            return res;
    };

    var firstUniqChar = function(s) {
        var str = s.toLowerCase();
        for(var i=0;i<str.length;i++){
            var ch = str.charAt(i);
            //如果后面没有该字符，且前面也没有出现过
            if(str.indexOf(ch) == i && str.lastIndexOf(ch) == i){
                return i;
            }
        }
        return -1;
    };

    var isAnagram = function(s, t) {
        var codeMap = {};
        if(s.length !== t.length) return false;
        for(var i=0; i<s.length; i++){
            var code = s.charCodeAt(i)
            codeMap[code] = codeMap[code] ? ++codeMap[code] : 1;
        }
        for(var i=0; i<t.length; i++){
            var code = t.charCodeAt(i)
            if(!codeMap[code]) return false;
            codeMap[code]--;
        }
        for(var i in codeMap){
            if(codeMap[code] !== 0) return false;
        }
        return true
    };