# 7. Reverse Integer

# Tags

1. String

Reverse digits of an integer.

Example1: x = 123, return 321

Example2: x = -123, return -321

Have you thought about this?

Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!

If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.

Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of 1000000003 overflows. How should you handle such cases?

For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

# 题意：

求整数的反向数字

# 分析

题目很简单，就是数字每位的数字左右取反，值得注意的是题目加了边界值，提示中已经说了关键信息 32-bit integer，Max是2³¹.剩下的注意一下正负号即可。

# 思路：

1. 将数字取正，然后反向（具体方法见代码）
2. 判断正负，添加符号
3. 判断是否越界，按照提示越界就返回0

# Js实现：

# 复杂度：

时间复杂度O(n)

/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
    let Max = 2147483648;
    let abs = Math.abs(x)
    let res = 0;
    while(abs!==0) {
        res = res*10+abs%10;
        abs = Math.floor(abs/10);
    }
    if(x < 0) {
        res = -res;
    }
    if(res > Max || res < -Max) {
        return 0;
    }

    return res;
};