reverse-integer.js

/**
 * Source:  https://leetcode.com/problems/reverse-integer/
 * Tags:    [Math]
 * Level:   Easy
 * Updated: 2015-04-24
 * Title:   Reverse Integer
 * Auther:  @imcoddy
 * Content: Reverse digits of an integer.
 *
 *
 * Example1: x =  123, return  321
 * Example2: x = -123, return -321
 *
 *
 * click to show spoilers.
 *
 * Have you thought about this?
 *
 * Here are some good questions to ask before coding. Bonus points for you if you have already thought through this!
 *
 * If the integer's last digit is 0, what should the output be? ie, cases such as 10, 100.
 *
 * Did you notice that the reversed integer might overflow? Assume the input is a 32-bit integer, then the reverse of 1000000003 overflows. How should you handle such cases?
 *
 * For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
 *
 *
 * Update (2014-11-10):
 * Test cases had been added to test the overflow behavior.
 */

/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
    var negative = false;
    var result = 0;
    var MAX = 2147483647;
    if (x < 0) {
        negative = true;
        x = -x;
    }

    var str = '' + x;
    var digits = str.split('');

    for (var i = digits.length - 1; i >= 0; i--) {
        result = result * 10 + parseInt(digits[i]);
    }

    if (result > MAX) {
        // Overflow as 32-bit integer
        result = 0;
    }
    return negative ? -result : result;
};


console.log(reverse(123));
console.log(reverse(100));
console.log(reverse(10001));
console.log(reverse(1000000003));
console.log(reverse(-123));
console.log(reverse(-100));