[LeetCode] 9. Palindrome Number

Posted 2021-03-15 aaronliu1991

回文数。题意是判断一个数字是否是回文数。这个题跟第7题非常类似，几乎是一样的做法。例子，

Example 1:

Input: 121
Output: true

Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

首先负数一定不是回文数，其次回文数一定不会越界所以少一些判断。代码如下，

时间O(n)

空间O(1)

 1 /**
 2  * @param {number} x
 3  * @return {boolean}
 4  */
 5 var isPalindrome = function(x) {
 6     // corner case
 7     if (x < 0 || (x !== 0 && x % 10 === 0)) return false;
 8 
 9     // normal case
10     let palindrome = x;
11     let reverse = 0;
12     while (x > 0) {
13         reverse = reverse * 10 + (x % 10);
14         x = ~~(x / 10);
15     }
16     return palindrome === reverse;
17 };