LeetCode Palidrome Number

class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0) return false;
        int pow = 1;
        int t = x;
        int cnt = 1;
        while(t /= 10) {
            pow *= 10;
            cnt++;
        }
        t = x;
        cnt = cnt / 2;
        while (cnt--) {
            if ((t / pow % 10) != t % 10) return false;
            t = t / 10;
            pow /= 100;
        }
        return true;
    }
};

500ms+,怎么会那么长时间

第二轮：

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

还是出了点差错，负数不算回文

// 19:50
class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0) return false;
        int n = x;
        int cnt = 0;
        
        do {
            cnt++;
            x = x/10;
        } while (x);
        
        int tens = 1;
        for (int i=1; i<cnt; i++) {
            tens = tens*10;
        }
        
        for (int i=cnt/2-1; i>=0; i--) {
            int a = n / tens;
            int b = n % 10;
            n = n - a * tens;
            n = n / 10;
            if (a != b) {
                return false;
            }
            tens = tens/100;
        }
        return true;
    }
};