Introduction

In this blog post, we will explore how to solve the LeetCode problem "3113" 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 array of positive integers nums. Return the number of subarrays of nums, where the first and the last elements of the subarray are equal to the largest element in the subarray. Example 1: Input: nums = [1,4,3,3,2] Output: 6 Explanation: There are 6 subarrays which have the first and the last elements equal to the largest element of the subarray: subarray [1,4,3,3,2], with its largest element 1. The first element is 1 and the last element is also 1. subarray [1,4,3,3,2], with its largest element 4. The first element is 4 and the last element is also 4. subarray [1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3. subarray [1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3. subarray [1,4,3,3,2], with its largest element 2. The first element is 2 and the last element is also 2. subarray [1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3. Hence, we return 6. Example 2: Input: nums = [3,3,3] Output: 6 Explanation: There are 6 subarrays which have the first and the last elements equal to the largest element of the subarray: subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. subarray [3,3,3], with its largest element 3. The first element is 3 and the last element is also 3. Hence, we return 6. Example 3: Input: nums = [1] Output: 1 Explanation: There is a single subarray of nums which is [1], with its largest element 1. The first element is 1 and the last element is also 1. Hence, we return 1. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109

Explanation

Here's a breakdown of the solution, followed by the Python code:

• Approach: Iterate through all possible subarrays. For each subarray, find its maximum element. Check if the first and last elements of the subarray are equal to this maximum. If they are, increment the count.
• Optimization: No specific optimization is required, as the problem constraints (array length up to 10^5) allow for a simple brute-force approach within the time limit.
• Complexity:
  • Runtime: O(n^2), where n is the length of the input array (due to nested loops for generating subarrays).
  • Storage: O(1), constant extra space.

Code

    def count_subarrays(nums):
    """
    Counts the number of subarrays where the first and last elements are equal to the largest element in the subarray.

    Args:
        nums: A list of positive integers.

    Returns:
        The number of subarrays that satisfy the condition.
    """

    count = 0
    n = len(nums)

    for i in range(n):
        for j in range(i, n):
            subarray = nums[i:j+1]
            max_val = max(subarray)
            if subarray[0] == max_val and subarray[-1] == max_val:
                count += 1

    return count