LeetCode 7. Reverse Integer

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Example 1:

Input: x = 123
Output: 321

Example 2:

Input: x = -123
Output: -321

Example 3:

Input: x = 120
Output: 21

Example 4:

Input: x = 0
Output: 0

Constraints:

• -2^31 <= x <= 2^31 - 1

Solution:

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class Solution {
public:
    int reverse(int x) {
        // INT_MAX: 2147483647
        // INT_MIN: -2147483648
        int result = 0;
        
        while (x != 0) {
            int mod = x % 10;
            
            if (result > 214748364 || (result == 214748364 && mod > 7)) {
                return 0;
            }
            if (result < -214748364 || (result == -214748364 && mod == -9)) {
                return 0;
            }
            
            result = 10 * result + mod;
            x /= 10;
        }
        
        return result;
    }
};