Javascript Interview Question:Reverse Number

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:

-2**31 <= x <= 2**31 - 1

Solution(converting number to string then reverse):

let x = -123;

var reverse = function (x) {

let reversedAbs= Math.sign(x) * parseInt(Math.abs(x).toString().split('').reverse().join(''))

return ( -1 * 2 ** 31 > reversedAbs || 2 ** 31 - 1 < reversedAbs) ? 0:reversedAbs

};

let reversedAbs = reverse(x);

console.log(reversedAbs);

Output:

-321

Solution(using maths modulo operator):

let x = -123;

var reverse = function (x) {

let y = Math.abs(x);

let reversedAbs = 0;

let lowerBound = -1 * 2 ** 31;

let upperBound = 2 ** 31 - 1;

while (y > 0) {

reversedAbs = reversedAbs * 10 + (y % 10);

if (lowerBound > reversedAbs || upperBound < reversedAbs) {

return 0;

}

y = Math.floor(y / 10);

}

reversedAbs = Math.sign(x) * reversedAbs;

if (lowerBound > reversedAbs || upperBound < reversedAbs) {

return 0;

} else {

return reversedAbs;

}

};

let reversedAbs = reverse(x);

console.log(reversedAbs);

Output:

-321