Introduction

In this blog post, we will explore how to solve the LeetCode problem "1331" 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 an array of integers arr, replace each element with its rank. The rank represents how large the element is. The rank has the following rules: Rank is an integer starting from 1. The larger the element, the larger the rank. If two elements are equal, their rank must be the same. Rank should be as small as possible. Example 1: Input: arr = [40,10,20,30] Output: [4,1,2,3] Explanation: 40 is the largest element. 10 is the smallest. 20 is the second smallest. 30 is the third smallest. Example 2: Input: arr = [100,100,100] Output: [1,1,1] Explanation: Same elements share the same rank. Example 3: Input: arr = [37,12,28,9,100,56,80,5,12] Output: [5,3,4,2,8,6,7,1,3] Constraints: 0 <= arr.length <= 105 -109 <= arr[i] <= 109

Explanation

Here's a solution to the problem, incorporating efficiency and optimality:

• Deduplication and Sorting: Remove duplicate elements while preserving their order of appearance to establish a unique ranking sequence. Then, sort this unique sequence to determine the ranks.
• Rank Assignment: Create a dictionary to store the rank of each unique element based on its sorted position.

• Rank Replacement: Iterate through the original array and replace each element with its corresponding rank from the dictionary.

• Time Complexity: O(n log n), due to sorting. Space Complexity: O(n), in the worst case where all elements are distinct.

Code

    def arrayRankTransform(arr):
    """
    Transforms an array by replacing each element with its rank.

    Args:
        arr (List[int]): The input array of integers.

    Returns:
        List[int]: The transformed array with ranks.
    """
    if not arr:
        return []

    # Create a sorted list of unique elements to determine ranks
    unique_nums = []
    seen = set()
    for num in arr:
        if num not in seen:
            unique_nums.append(num)
            seen.add(num)

    sorted_nums = sorted(unique_nums)

    # Create a dictionary to store the rank of each unique element
    rank_map = {}
    for i, num in enumerate(sorted_nums):
        rank_map[num] = i + 1

    # Replace each element in the original array with its rank
    ranked_arr = [rank_map[num] for num in arr]

    return ranked_arr