7 整数反转

https://leetcode.cn/leetbook/read/top-interview-questions-easy/xnx13t/

https://leetcode.cn/problems/reverse-integer/description/

cost: 10m58s

class Solution {
public:
    int reverse(int x) {
        if (x < 0) {
            if (x == (-0x7FFFFFFF - 1)) {
                return 0;
            }
            return -this->reverse(-x);
        }
        int threshold = 0x7FFFFFFF / 10;
        int r = 0;
        while (x > 0) {
            if (r > threshold) {
                return 0;
            }
            r *= 10;
            r += x % 10;
            x /= 10;
        }
        return r;
    }
};

• 时间复杂度：O(log(n))
• 空间复杂度：O(1)