7. Reverse Integer

Problem Statement

Medium

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

Constraints:

-2³¹ <= x <= 2³¹ - 1

C++

Source file

class Solution {
public:
    int reverse(int x) {
        long ans = 0;
        while(x){
            int D = x%10;
            ans = ans*10 + D;
            if(ans>INT_MAX || ans<INT_MIN)
                return 0;
            x /= 10;
        }
        return (int)ans;
    }
};

Java

Source file

class Solution {
    public int reverse(int x) {
        int rev = 0, lastValidNum = Integer.MAX_VALUE / 10;
        boolean negative = x < 0;
        x = Math.abs(x);
        while (x > 0) {
            if (rev > lastValidNum)
                return 0;
            rev *= 10;
            rev += x % 10;
            x /= 10;
        }
        return negative ? -rev : rev;
    }
}