RotatedDigits.js

// Source : https://leetcode.com/problems/rotated-digits
// Author : Dean Shi
// Date   : 2018-03-10

/***************************************************************************************
 * X is a good number if after rotating each digit individually by 180 degrees, we get
 * a valid number that is different from X.  Each digit must be rotated - we cannot
 * choose to leave it alone.
 *
 * A number is valid if each digit remains a digit after rotation. 0, 1, and 8 rotate
 * to themselves; 2 and 5 rotate to each other; 6 and 9 rotate to each other, and the
 * rest of the numbers do not rotate to any other number and become invalid.
 *
 * Now given a positive number N, how many numbers X from 1 to N are good?
 *
 * Example:
 * Input: 10
 * Output: 4
 * Explanation:
 * There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
 * Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
 *
 * Note:
 *
 * N  will be in range [1, 10000].
 *
 ***************************************************************************************/

/**
 * @param {number} N
 * @return {number}
 */
var rotatedDigits = function(N) {
    const validNumArr = ['2', '5', '6', '9']
    const invalidNumArr = ['3', '4', '7']
    let sum = 0

    for (let i = 1; i <= N; i++) {
        const strNum = String(i)
        if (
            !invalidNumArr.some((n) => strNum.includes(n)) &&
            validNumArr.some((n) => strNum.includes(n))
        ) sum++
    }
    return sum
};