[leetcode] 7. 整数反转

2^31-1=2147483647,-2^31=-2147483648

参考：

https://leetcode-cn.com/problems/reverse-integer/solution/zheng-shu-fan-zhuan-by-leetcode/

class Solution {
public:
    int reverse(int x) {
        int rev = 0;
        while (x != 0) {
            int pop = x % 10;
            x /= 10;
            if (rev > INT_MAX/10 || (rev == INT_MAX / 10 && pop > 7)) return 0;
            if (rev < INT_MIN/10 || (rev == INT_MIN / 10 && pop < -8)) return 0;
            rev = rev * 10 + pop;
        }
        return rev;
    }
};