Introduction

In this blog post, we will explore how to solve the LeetCode problem "2367" 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 a 0-indexed, strictly increasing integer array nums and a positive integer diff. A triplet (i, j, k) is an arithmetic triplet if the following conditions are met: i < j < k, nums[j] - nums[i] == diff, and nums[k] - nums[j] == diff. Return the number of unique arithmetic triplets. Example 1: Input: nums = [0,1,4,6,7,10], diff = 3 Output: 2 Explanation: (1, 2, 4) is an arithmetic triplet because both 7 - 4 == 3 and 4 - 1 == 3. (2, 4, 5) is an arithmetic triplet because both 10 - 7 == 3 and 7 - 4 == 3. Example 2: Input: nums = [4,5,6,7,8,9], diff = 2 Output: 2 Explanation: (0, 2, 4) is an arithmetic triplet because both 8 - 6 == 2 and 6 - 4 == 2. (1, 3, 5) is an arithmetic triplet because both 9 - 7 == 2 and 7 - 5 == 2. Constraints: 3 <= nums.length <= 200 0 <= nums[i] <= 200 1 <= diff <= 50 nums is strictly increasing.

Explanation

Here's a breakdown of the solution:

• Hashing for Efficient Lookup: Utilize a set (or hash table) to store all numbers in nums. This enables O(1) average time complexity for checking if a number exists in the array.
• Iterate and Check: Iterate through the nums array. For each number, check if num + diff and num + 2*diff are present in the set. If both exist, increment the count of arithmetic triplets.

• Uniqueness: Since nums is strictly increasing, the triplets found will automatically be unique, satisfying the i < j < k condition.

• Runtime Complexity: O(n), where n is the length of nums.

• Storage Complexity: O(n), where n is the length of nums (due to the set).

Code

    def arithmeticTriplets(nums: list[int], diff: int) -> int:
    """
    Finds the number of unique arithmetic triplets in a strictly increasing array.

    Args:
        nums: A 0-indexed, strictly increasing integer array.
        diff: A positive integer representing the difference between elements in the triplet.

    Returns:
        The number of unique arithmetic triplets.
    """
    count = 0
    num_set = set(nums)

    for num in nums:
        if (num + diff) in num_set and (num + 2 * diff) in num_set:
            count += 1

    return count