LeetCode 9. Palindrome Number

发表于 | 分类于 |

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Follow up: Could you solve it without converting the integer to a string?

Example 1:
Input: x = 121
Output: true

Example 2:
Input: x = -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: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Example 4:
Input: x = -101
Output: false

Constraints:
-2^31 <= x <= 2^31 - 1

思路:
要验证回文数，那么就需要看前后半段是否对称，如果把后半段翻转一下，就看和前半段是否相等就行了，所以做法就是取出后半段数字，进行翻转。

Solution:

1
2
3
4
5
6
7
8
9
10
11
class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0 || (x % 10 == 0 && x != 0)) return false;
        int revertNum = 0;
        while (x > revertNum) {
            revertNum = revertNum * 10 + x % 10;
            x /= 10;
        }
        return x == revertNum || x == revertNum / 10;
    }
}