# 9. Palindrome Number

# Tags

1. Math

Determine whether an integer is a palindrome. Do this without extra space.

Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

# 题意：

判断一个整数是否是回文，不能使用额外空间

# 分析：

此题与题7.Reverse Integer 类似，做法也类似，都是将数字反向颠倒过来比较是否相等即可。

# 思路：

1. 取传入数字的绝对值，反向颠倒（注：负数不是回文）
2. 比较跟原值是否相等，相等就是回文，不等就不是

# Js实现：

# 复杂度

时间复杂度O(n)

/**
 * @param {number} x
 * @return {boolean}
 */
var isPalindrome = function(x) {
    let res = 0;
    let abs = Math.abs(x);
    while(abs !== 0) {
        res = res*10 + abs % 10;
        abs = Math.floor(abs / 10);
    }
    return res===x;
};