[LeetCode] 1710. Maximum Units on a Truck

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 <= 106

卡车上的最大单元数。

请你将一些箱子装在 一辆卡车 上。给你一个二维数组 boxTypes ，其中 boxTypes[i] = [numberOfBoxesi, numberOfUnitsPerBoxi] ：

numberOfBoxesi 是类型 i 的箱子的数量。
numberOfUnitsPerBoxi 是类型 i 每个箱子可以装载的单元数量。
整数 truckSize 表示卡车上可以装载 箱子 的 最大数量 。只要箱子数量不超过 truckSize ，你就可以选择任意箱子装到卡车上。

返回卡车可以装载 单元 的 最大 总数。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/maximum-units-on-a-truck
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思路是贪心。题设给的是不同类型的箱子，box[i][j] 中 i 代表此类型的箱子有几个，j 代表此类型的箱子里有几样东西。首先我们把 input 根据 j 从大到小排序，这样箱子内东西多的就在前。接着我们遍历 input 数组，当卡车还装得下的情况下（truckSize > 0），我们试图把当前类型的箱子一个个放入，直到当前的箱子被用完或者卡车装不下为止。

时间O(nlogn)

空间O(1)

Java实现

class Solution {
    public int maximumUnits(int[][] boxTypes, int truckSize) {
        Arrays.sort(boxTypes, (a, b) -> b[1] - a[1]);
        int sum = 0;
        for (int i = 0; i < boxTypes.length; i++) {
            while (truckSize > 0 && boxTypes[i][0] > 0) {
                sum += boxTypes[i][1];
                truckSize--;
                boxTypes[i][0]--;
            }
        }
        return sum;
    }
}

LeetCode 题目总结