Introduction

In this blog post, we will explore how to solve the LeetCode problem "2784" 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. We consider an array good if it is a permutation of an array base[n]. base[n] = [1, 2, ..., n - 1, n, n] (in other words, it is an array of length n + 1 which contains 1 to n - 1 exactly once, plus two occurrences of n). For example, base[1] = [1, 1] and base[3] = [1, 2, 3, 3]. Return true if the given array is good, otherwise return false. Note: A permutation of integers represents an arrangement of these numbers. Example 1: Input: nums = [2, 1, 3] Output: false Explanation: Since the maximum element of the array is 3, the only candidate n for which this array could be a permutation of base[n], is n = 3. However, base[3] has four elements but array nums has three. Therefore, it can not be a permutation of base[3] = [1, 2, 3, 3]. So the answer is false. Example 2: Input: nums = [1, 3, 3, 2] Output: true Explanation: Since the maximum element of the array is 3, the only candidate n for which this array could be a permutation of base[n], is n = 3. It can be seen that nums is a permutation of base[3] = [1, 2, 3, 3] (by swapping the second and fourth elements in nums, we reach base[3]). Therefore, the answer is true. Example 3: Input: nums = [1, 1] Output: true Explanation: Since the maximum element of the array is 1, the only candidate n for which this array could be a permutation of base[n], is n = 1. It can be seen that nums is a permutation of base[1] = [1, 1]. Therefore, the answer is true. Example 4: Input: nums = [3, 4, 4, 1, 2, 1] Output: false Explanation: Since the maximum element of the array is 4, the only candidate n for which this array could be a permutation of base[n], is n = 4. However, base[4] has five elements but array nums has six. Therefore, it can not be a permutation of base[4] = [1, 2, 3, 4, 4]. So the answer is false. Constraints: 1 <= nums.length <= 100 1 <= num[i] <= 200

Explanation

Here's the breakdown of the solution:

• Determine n: Find the maximum element in the nums array. This value becomes our candidate for n.
• Length Check: Verify if the length of nums is equal to n + 1. If not, the array cannot be a permutation of base[n].

• Frequency Check: Count the occurrences of each number from 1 to n in nums. Ensure that each number from 1 to n-1 appears exactly once, and n appears twice.

• Runtime Complexity: O(n)

• Storage Complexity: O(n)

Code

    def isGood(nums):
    """
    Checks if the given array is a permutation of base[n].

    Args:
        nums (list of int): The input array.

    Returns:
        bool: True if the array is good, False otherwise.
    """

    n = max(nums)
    if len(nums) != n + 1:
        return False

    counts = {}
    for num in nums:
        counts[num] = counts.get(num, 0) + 1

    for i in range(1, n):
        if counts.get(i, 0) != 1:
            return False

    if counts.get(n, 0) != 2:
        return False

    return True