How do you solve Max Sum of a Pair With Equal Sum of Digits on LeetCode?

Max Sum of a Pair With Equal Sum of Digits (LeetCode #2342) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Grouping numbers by their digit sums allows for efficient pair searching.

What is the brute force solution for Max Sum of a Pair With Equal Sum of Digits?

The brute force approach for Max Sum of a Pair With Equal Sum of Digits is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach checks every possible pair of indices in the array to see if their digit sums match. If they do, we calculate their sum and keep track of the maximum found. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Max Sum of a Pair With Equal Sum of Digits?

Max Sum of a Pair With Equal Sum of Digits uses the following concepts: Array, Hash Table, Sorting, Heap (Priority Queue). The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Max Sum of a Pair With Equal Sum of Digits?

Always think about how to reduce the number of comparisons needed. Explain your thought process clearly while coding; it helps the interviewer understand your approach. Consider edge cases, such as arrays with no valid pairs.

What are common mistakes when solving Max Sum of a Pair With Equal Sum of Digits?

Not considering the case where no valid pairs exist and returning -1. Failing to handle large inputs efficiently, leading to timeouts.

#2342

Max Sum of a Pair With Equal Sum of Digits

Medium

ArrayHash TableSortingHeap (Priority Queue)Hash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

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Intuition

Time O(n)Space O(n)

Instead of checking all pairs, we can group numbers by their digit sums using a hash map. This allows us to efficiently find the two largest numbers for each digit sum and compute their maximum sum.

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Algorithm

4 steps

1Step 1: Create a hash map to store the largest two numbers for each digit sum.
2Step 2: Iterate through the array and calculate the digit sum for each number.
3Step 3: Update the hash map with the two largest numbers for each digit sum.
4Step 4: After processing all numbers, find the maximum sum from the values in the hash map.

solution.py22 lines

1# Full working Python code
2
3def digit_sum(n):
4    return sum(int(d) for d in str(n))
5
6def max_sum_of_pairs(nums):
7    from collections import defaultdict
8    digit_map = defaultdict(list)
9    for num in nums:
10        d_sum = digit_sum(num)
11        digit_map[d_sum].append(num)
12        if len(digit_map[d_sum]) > 2:
13            digit_map[d_sum].sort(reverse=True)
14            digit_map[d_sum] = digit_map[d_sum][:2]
15    max_sum = -1
16    for values in digit_map.values():
17        if len(values) == 2:
18            max_sum = max(max_sum, sum(values))
19    return max_sum
20
21# Example usage
22print(max_sum_of_pairs([18, 43, 36, 13, 7]))  # Output: 54

ℹ

Complexity note: This complexity is due to a single pass through the array to compute digit sums and store them, leading to O(n) time. The space complexity arises from storing the numbers in the hash map.

1Grouping numbers by their digit sums allows for efficient pair searching.
2Using a hash map can significantly reduce the number of comparisons needed.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.