0007-reverse-integer.js

/**
 * https://leetcode.com/problems/reverse-integer/
 * Time O(log(x)) | Space O(1)
 * @param {number} x
 * @return {number}
 */
var reverse = function (x, result = 0) {
    while (x !== 0) {
        const digit = x % 10;

        if (isOutOfBounds(digit, result)) return 0;

        x = Math.trunc(x / 10);
        result = result * 10 + digit;
    }

    return result;
};

const isOutOfBounds = (digit, result) => {
    const [max, min] = [2 ** 31 - 1, -(2 ** 31)];
    const [maxProduct, maxRemainder] = [max / 10, max % 10];
    const [minProduct, minRemainder] = [min / 10, min % 10];
    const isTarget = result === maxProduct;

    const isMaxOut = maxProduct < result || (isTarget && maxRemainder <= digit);
    const isMinOut = result < minProduct || (isTarget && digit <= minRemainder);

    return isMaxOut || isMinOut;
};