1710. Maximum Units on a Truck

Problem

Tags: Array, Greedy, Sorting

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

• numberOfBoxesi is the number of boxes of type i.
• numberOfUnitsPerBoxi 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 <= numberOfBoxesi, numberOfUnitsPerBoxi <= 1000
• 1 <= truckSize <= 10^6

Code

JS

// 1710. Maximum Units on a Truck (8/6/53421)
// Runtime: 84 ms (78.41%) Memory: 40.96 MB (94.90%) 

/**
 * @param {number[][]} boxTypes
 * @param {number} truckSize
 * @return {number}
 */
var maximumUnits = function(boxTypes, truckSize) {
    // 已經在車上的總箱子數與總單元數
    let total_boxes = 0, total_units = 0;
    
    // 依單一箱子容量來排序箱子種類
    boxTypes.sort((a, b) => b[1] - a[1]);
    
    // 從單一箱子容量最大來遍歷箱子種類
    for(let i = 0; i < boxTypes.length; i++) {
        // 車上還剩多少可以放箱子的空間
        let space = truckSize - total_boxes;
        
        if(space >= boxTypes[i][0]) {
            // 如果空間來足以將所有此種箱子放入，則放入所有此種箱子
            total_boxes += boxTypes[i][0];
            total_units += boxTypes[i][0] * boxTypes[i][1];
        }
        else {
            // 如果空間不足將所有此種箱子放入，則以此種箱子填滿剩餘空間
            total_units += space * boxTypes[i][1];
            break;
        }
    }
    
    return total_units;
};