Formatted question description: https://leetcode.ca/all/1710.html

1710. Maximum Units on a Truck

Level

Easy

Description

You are assigned to put some amount of boxes onto one truck. You are given a 2D array boxTypes, where boxTypes[i] = [numberOfBoxes_i, numberOfUnitsPerBox_i]:

  • numberOfBoxes_i is the number of boxes of type i.
  • numberOfUnitsPerBox_i is the number of units in each box of the type i.

You are also given an integer truckSize, which is the maximum number of boxes that can be put on the truck. You can choose any boxes to put on the truck as long as the number of boxes does not exceed truckSize.

Return the maximum total number of units that can be put on the truck.

Example 1:

Input: boxTypes = [[1,3],[2,2],[3,1]], truckSize = 4

Output: 8

Explanation: There are:

  • 1 box of the first type that contains 3 units.
  • 2 boxes of the second type that contain 2 units each.
  • 3 boxes of the third type that contain 1 unit each.

You can take all the boxes of the first and second types, and one box of the third type.

The total number of units will be = (1 * 3) + (2 * 2) + (1 * 1) = 8.

Example 2:

Input: boxTypes = [[5,10],[2,5],[4,7],[3,9]], truckSize = 10

Output: 91

Constraints:

  • 1 <= boxTypes.length <= 1000
  • 1 <= numberOfBoxes_i, numberOfUnitsPerBox_i <= 1000
  • 1 <= truckSize <= 10^6

Solution

Sort boxTypes according to number of units in descending order and then according to number of boxes in descending order. Loop over the sorted boxTypes and select the first truckSize boxes with maximum units. Calculate the sum of units of the selected boxes and return.

class Solution {
    public int maximumUnits(int[][] boxTypes, int truckSize) {
        Arrays.sort(boxTypes, new Comparator<int[]>() {
            public int compare(int[] boxType1, int[] boxType2) {
                if (boxType1[1] != boxType2[1])
                    return boxType2[1] - boxType1[1];
                else
                    return boxType2[0] - boxType1[0];
            }
        });
        int boxes = 0;
        int maxUnits = 0;
        int length = boxTypes.length;
        for (int i = 0; i < length && boxes < truckSize; i++) {
            int[] boxType = boxTypes[i];
            int num = boxType[0], units = boxType[1];
            num = Math.min(num, truckSize - boxes);
            boxes += num;
            maxUnits += units * num;
        }
        return maxUnits;
    }
}

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