7. Reverse Integer

https://leetcode.com/problems/reverse-integer/

Problem

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321

Example 2:

Input: -123
Output: -321

Example 3:

Input: 120
Output: 21

Note: Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

Solution

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

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