Introduction

In this blog post, we will explore how to solve the LeetCode problem "2729" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given an integer n that consists of exactly 3 digits. We call the number n fascinating if, after the following modification, the resulting number contains all the digits from 1 to 9 exactly once and does not contain any 0's: Concatenate n with the numbers 2 n and 3 n. Return true if n is fascinating, or false otherwise. Concatenating two numbers means joining them together. For example, the concatenation of 121 and 371 is 121371. Example 1: Input: n = 192 Output: true Explanation: We concatenate the numbers n = 192 and 2 n = 384 and 3 n = 576. The resulting number is 192384576. This number contains all the digits from 1 to 9 exactly once. Example 2: Input: n = 100 Output: false Explanation: We concatenate the numbers n = 100 and 2 n = 200 and 3 n = 300. The resulting number is 100200300. This number does not satisfy any of the conditions. Constraints: 100 <= n <= 999

Explanation

Here's a solution to determine if a 3-digit number is fascinating, along with an explanation of the approach and complexity analysis.

• Concatenate and Convert: Calculate 2*n and 3*n, concatenate n, 2*n, and 3*n into a single string.
• Digit Frequency Check: Check if the concatenated string's length is 9 and if it contains unique digits from '1' to '9'.

• Boolean Return: Return True if the above conditions are met; otherwise, return False.

• Time Complexity: O(1), Space Complexity: O(1) - The operations are performed on a fixed number of digits and constant-size data structures.

Code

    def is_fascinating(n: int) -> bool:
    """
    Determines if a 3-digit number n is fascinating.

    A number n is fascinating if concatenating n, 2*n, and 3*n contains
    all digits from 1 to 9 exactly once and no 0s.

    Args:
        n: A 3-digit integer.

    Returns:
        True if n is fascinating, False otherwise.
    """

    s = str(n) + str(2 * n) + str(3 * n)
    if len(s) != 9:
        return False

    digits = set(s)
    if len(digits) != 9:
        return False

    for digit in digits:
        if digit == '0':
            return False

    for i in range(1, 10):
        if str(i) not in s:
            return False

    return True