Rotated Digits

Problem statement

An integer x is a good 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. For example:

• 0, 1, and 8 rotate to themselves,
• 2 and 5 rotate to each other (in this case they are rotated in a different direction, in other words, 2 or 5 gets mirrored),
• 6 and 9 rotate to each other, and
• the rest of the numbers do not rotate to any other number and become invalid.

Given an integer n, return the number of good integers in the range [1, n].

Example 1:

Input: n = 10Output: 4Explanation: 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.

Example 2:

Input: n = 1Output: 0

Example 3:

Input: n = 2Output: 1

Constraints:

• 1 <= n <= 104

My solution

/**
 * @param {number} n
 * @return {number}
 */
var rotatedDigits = function(n) {
    let count = 0;
    for (let i = 1; i <= n; i++) {
        if (isValid(i)) {
            count++
        }
    }
    
    return count
};

function isValid(n) {
    let isValid = false;
    while (n) {
        const compare = n % 10;
        if (compare === 3 || compare === 4 || compare === 7) {
            return false;
        }
        if (compare === 2 || compare === 5 || compare === 6 || compare === 9) {
            isValid = true
        }
        n = Math.trunc(n / 10)
    }
    return isValid;
}