9. Palindrome Number

O(1) time O(1) space

class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x == 0: return True
        if x < 0 or x % 10 == 0: return False
        y = 0
        while x > y:
            y = y * 10 + x % 10
            x //= 10
        return x == y or x == y // 10

class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0 || x != 0 && x % 10 == 0) return false; // 负数和结尾是0的正数都不合法
        int y = 0;
        while (x > y) {
            y = y * 10 + x % 10;
            x /= 10;
        }
        return x == y || x == y / 10;
    }
};