Introduction

In this blog post, we will explore how to solve the LeetCode problem "2501" 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 array nums. A subsequence of nums is called a square streak if: The length of the subsequence is at least 2, and after sorting the subsequence, each element (except the first element) is the square of the previous number. Return the length of the longest square streak in nums, or return -1 if there is no square streak. A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: nums = [4,3,6,16,8,2] Output: 3 Explanation: Choose the subsequence [4,16,2]. After sorting it, it becomes [2,4,16]. - 4 = 2 2. - 16 = 4 4. Therefore, [4,16,2] is a square streak. It can be shown that every subsequence of length 4 is not a square streak. Example 2: Input: nums = [2,3,5,6,7] Output: -1 Explanation: There is no square streak in nums so return -1. Constraints: 2 <= nums.length <= 105 2 <= nums[i] <= 105

Explanation

Here's a solution to find the longest square streak in an array, along with an explanation:

• High-Level Approach:

  • Use a hash set to efficiently check for the presence of numbers in the input array.
  • Iterate through the input array. For each number, attempt to build a square streak starting with that number.
  • Keep track of the length of the longest square streak found so far.

• Complexity:

  • Runtime Complexity: O(n log(max(nums))), where n is the length of nums. The log factor comes from potentially looking up the square root repeatedly to construct the streak. The set lookups are O(1) on average.
  • Storage Complexity: O(n) due to the set used to store the numbers.

Code

    def longest_square_streak(nums: list[int]) -> int:
    """
    Finds the length of the longest square streak in nums.

    Args:
        nums: An integer array.

    Returns:
        The length of the longest square streak in nums, or -1 if there is no square streak.
    """

    num_set = set(nums)
    max_streak = -1

    for num in nums:
        current_streak = 1
        next_num = num * num

        while next_num in num_set:
            current_streak += 1
            next_num = next_num * next_num
            if next_num > 100000:
                break

        if current_streak >= 2:
            max_streak = max(max_streak, current_streak)

    return max_streak