7. Reverse Integer (https://leetcode.com/problems/reverse-integer/): Given a 32-bit signed integer, reverse digits of an integer.

7. Reverse Integer (#1 Math).java

// Math solution: Pull the digits and take care of the overflow
// Time: O(logx), 1ms
// Space: O(1), 36.6mb
class Solution {
    public int reverse(int x) {
        int ans = 0;
        
        while(x != 0) {
            int tail = x % 10;
            int newAns = ans * 10 + tail;
            
            // !!: Take care the overflow by checking if result is as we expected when adding newAns
            if((newAns - tail) / 10 != ans) return 0;
            ans = newAns;
            
            x /= 10;
        }
        
        return ans;
    }
}