#1088 - Confusing Number II

Problem Description

A confusing number is a number that when rotated 180 degrees becomes a different number with each digit valid.

We can rotate digits of a number by 180 degrees to form new digits.

When 0, 1, 6, 8, and 9 are rotated 180 degrees, they become 0, 1, 9, 8, and 6 respectively.
When 2, 3, 4, 5, and 7 are rotated 180 degrees, they become invalid.

Note that after rotating a number, we can ignore leading zeros.

For example, after rotating 8000, we have 0008 which is considered as just 8.

Given an integer n, return the number of confusing numbers in the inclusive range [1, n].

Solution

/**
 * @param {number} n
 * @return {number}
 */
var confusingNumberII = function(n) {
  const validDigits = [0, 1, 6, 8, 9];
  const rotationMap = { 0: 0, 1: 1, 6: 9, 8: 8, 9: 6 };
  let count = 0;

  const maxLength = n.toString().length;

  for (let len = 1; len <= maxLength; len++) {
    dfs(0, 0, len);
  }

  return count;

  function isConfusing(num) {
    const original = num;
    let rotated = 0;

    while (num > 0) {
      const digit = num % 10;
      rotated = rotated * 10 + rotationMap[digit];
      num = Math.floor(num / 10);
    }

    return original !== rotated;
  }

  function dfs(current, length, targetLength) {
    if (length === targetLength) {
      if (current <= n && current > 0 && isConfusing(current)) {
        count++;
      }
      return;
    }

    for (const digit of validDigits) {
      if (current === 0 && digit === 0) continue;
      const next = current * 10 + digit;
      if (next > n) break;
      dfs(next, length + 1, targetLength);
    }
  }
};