LeetCode 2815: Max Pair Sum in an Array Solution

Master LeetCode problem 2815 (Max Pair Sum in an Array), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2815. Max Pair Sum in an Array

Easy

Array Hash Table

Problem Explanation

Explanation

To solve this problem, we can iterate through the array and keep track of the maximum sum achievable with each largest digit encountered. We can store the maximum sum for each largest digit in a map or an array. Finally, we return the maximum sum from the map/array.

Create a map or an array to store the maximum sum for each largest digit.
Iterate through the array and for each number, find the largest digit.
Update the maximum sum for that largest digit with the current number if it results in a larger sum.
Return the maximum sum from the map/array.

Time Complexity: O(n), where n is the number of elements in the array. Space Complexity: O(1) since we are using a fixed-size map or array to store maximum sums for largest digits.

Solution Code

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int maxPairSum(int[] nums) {
        Map<Integer, Integer> maxSums = new HashMap<>();
        int maxSum = -1;

        for (int num : nums) {
            int largestDigit = 0;
            int temp = num;
            while (temp > 0) {
                largestDigit = Math.max(largestDigit, temp % 10);
                temp /= 10;
            }

            if (!maxSums.containsKey(largestDigit)) {
                maxSums.put(largestDigit, num);
            } else {
                maxSum = Math.max(maxSum, maxSums.get(largestDigit) + num);
                maxSums.put(largestDigit, Math.max(maxSums.get(largestDigit), num));
            }
        }

        return maxSum;
    }
}

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