Introduction

In this blog post, we will explore how to solve the LeetCode problem "967" 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

Given two integers n and k, return an array of all the integers of length n where the difference between every two consecutive digits is k. You may return the answer in any order. Note that the integers should not have leading zeros. Integers as 02 and 043 are not allowed. Example 1: Input: n = 3, k = 7 Output: [181,292,707,818,929] Explanation: Note that 070 is not a valid number, because it has leading zeroes. Example 2: Input: n = 2, k = 1 Output: [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98] Constraints: 2 <= n <= 9 0 <= k <= 9

Explanation

Here's the breakdown of the problem and the solution:

• High-Level Approach:

  • Use Depth-First Search (DFS) to explore all possible numbers of length n.
  • Start with each digit from 1 to 9 as the first digit (to avoid leading zeros).
  • Recursively build the number, ensuring the absolute difference between consecutive digits is k.

• Complexity:

  • Runtime Complexity: O(2ⁿ) (In the worst case, for each digit, we may have two choices if k is not 0.)
  • Storage Complexity: O(2ⁿ) (Space for the recursion stack and the result list, again as in worst case, all generated numbers satisfy the given criteria and are stored into the result)

Code

    def nums_same_consec_diff(n: int, k: int) -> list[int]:
    """
    Given two integers n and k, return an array of all the integers of length n
    where the difference between every two consecutive digits is k.
    You may return the answer in any order.
    Note that the integers should not have leading zeros.
    Integers as 02 and 043 are not allowed.

    Example 1:
    Input: n = 3, k = 7
    Output: [181,292,707,818,929]
    Explanation: Note that 070 is not a valid number, because it has leading zeroes.

    Example 2:
    Input: n = 2, k = 1
    Output: [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]

    Constraints:
    2 <= n <= 9
    0 <= k <= 9
    """

    result = []

    def dfs(num: int, length: int):
        if length == n:
            result.append(num)
            return

        last_digit = num % 10

        next_digits = []
        if last_digit + k <= 9:
            next_digits.append(last_digit + k)
        if k != 0 and last_digit - k >= 0:
            next_digits.append(last_digit - k)

        for next_digit in next_digits:
            dfs(num * 10 + next_digit, length + 1)

    for i in range(1, 10):
        dfs(i, 1)

    return result