LeetCode-in-Java

3462. Maximum Sum With at Most K Elements

Medium

You are given a 2D integer matrix grid of size n x m, an integer array limits of length n, and an integer k. The task is to find the maximum sum of at most k elements from the matrix grid such that:

• The number of elements taken from the ith row of grid does not exceed limits[i].

Return the maximum sum.

Example 1:

Input: grid = [[1,2],[3,4]], limits = [1,2], k = 2

Output: 7

Explanation:

• From the second row, we can take at most 2 elements. The elements taken are 4 and 3.
• The maximum possible sum of at most 2 selected elements is 4 + 3 = 7.

Example 2:

Input: grid = [[5,3,7],[8,2,6]], limits = [2,2], k = 3

Output: 21

Explanation:

• From the first row, we can take at most 2 elements. The element taken is 7.
• From the second row, we can take at most 2 elements. The elements taken are 8 and 6.
• The maximum possible sum of at most 3 selected elements is 7 + 8 + 6 = 21.

Constraints:

• n == grid.length == limits.length
• m == grid[i].length
• 1 <= n, m <= 500
• 0 <= grid[i][j] <= 105
• 0 <= limits[i] <= m
• 0 <= k <= min(n * m, sum(limits))

Solution

import java.util.Arrays;

public class Solution {
    public long maxSum(int[][] grid, int[] limits, int k) {
        int l = 0;
        for (int limit : limits) {
            l += limit;
        }
        int[] dp = new int[l];
        int a = 0;
        for (int i = 0; i < grid.length; i++) {
            int lim = limits[i];
            Arrays.sort(grid[i]);
            for (int j = grid[i].length - lim; j < grid[i].length; j++) {
                dp[a] = grid[i][j];
                a++;
            }
        }
        Arrays.sort(dp);
        long sum = 0L;
        for (int i = l - 1; i >= l - k; i--) {
            sum += dp[i];
        }
        return sum;
    }
}

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