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

JAVA

public class Solution {
		public int reverse(int x) {
			int result = 0;

			while (x != 0) {
				int tail = x % 10;
				int newResult = result * 10 + tail;

				// If overflow exists, the new result will not equal previous one.
				/*
					result = 998765432

					newResult = 1397719729 // here the program will do a cast, meaning overflow

				 */
				if ((newResult - tail) / 10 != result) {
					return 0;
				}

				result = newResult;

				x = x / 10;
			}

			return result;
		}
	}

C++

class Solution {






public:
    int reverse(int x) {
        if (x == INT_MIN) return 0;
        int r = 0, sign = x >= 0 ? 1 : -1, y = sign * x, p = 1;
        while (y) {
            y /= 10;
            if (y) p *= 10;
        }
        x = sign * x;
        while (x) {
            int d = x % 10;
            x /= 10;
            if ((INT_MAX - r) / p < d) return 0;
            r += p * d;
            p /= 10;
        }
        return sign * r;
    }
};

PYTHON

class Solution:
    





    def reverse(self, x: int) -> int:
        y = int(str(abs(x))[::-1])
        res = -y if x < 0 else y
        return 0 if res < -(2**31) or res > 2**31 - 1 else res

JAVASCRIPT

var reverse = 
    




    
    function (x) {
    let res = 0;
    while (x) {
        res = res * 10 + (x % 10);
        x = ~~(x / 10);
    }
    return res < Math.pow(-2, 31) || res > Math.pow(2, 31) - 1 ? 0 : res;
};