Introduction

In this blog post, we will explore how to solve the LeetCode problem "2815" 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. You have to find the maximum sum of a pair of numbers from nums such that the largest digit in both numbers is equal. For example, 2373 is made up of three distinct digits: 2, 3, and 7, where 7 is the largest among them. Return the maximum sum or -1 if no such pair exists. Example 1: Input: nums = [112,131,411] Output: -1 Explanation: Each numbers largest digit in order is [2,3,4]. Example 2: Input: nums = [2536,1613,3366,162] Output: 5902 Explanation: All the numbers have 6 as their largest digit, so the answer is 2536 + 3366 = 5902. Example 3: Input: nums = [51,71,17,24,42] Output: 88 Explanation: Each number's largest digit in order is [5,7,7,4,4]. So we have only two possible pairs, 71 + 17 = 88 and 24 + 42 = 66. Constraints: 2 <= nums.length <= 100 1 <= nums[i] <= 104

Explanation

• High-Level Approach: The solution involves iterating through the nums array, determining the largest digit in each number, and storing the numbers in a dictionary (hash map) where the key is the largest digit and the value is a list of numbers with that largest digit. Then, iterate through the dictionary and calculate the maximum sum for each group of numbers with the same largest digit.

• Complexity:
  • Runtime: O(N), where N is the number of elements in nums.
  • Storage: O(N), in the worst case where all numbers have different largest digits.

Code

    def maxSum(nums):
    """
    Finds the maximum sum of a pair of numbers from nums such that the largest digit in both numbers is equal.

    Args:
        nums: A list of integers.

    Returns:
        The maximum sum of a pair of numbers with the same largest digit, or -1 if no such pair exists.
    """

    digit_map = {}
    for num in nums:
        s_num = str(num)
        largest_digit = 0
        for digit in s_num:
            largest_digit = max(largest_digit, int(digit))

        if largest_digit not in digit_map:
            digit_map[largest_digit] = []
        digit_map[largest_digit].append(num)

    max_sum = -1
    for digit in digit_map:
        if len(digit_map[digit]) >= 2:
            numbers = digit_map[digit]
            numbers.sort(reverse=True)
            max_sum = max(max_sum, numbers[0] + numbers[1])

    return max_sum