7. Reverse Integer

Given a signed 32-bit integer x, return xwith 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

Constraints:

• -231 <= x <= 231 - 1

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

• T: $O(\log N)$
• S: $O(1)$