Table of contents
Problem:
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 typei
.numberOfUnitsPerBoxi
is the number of units in each box of the typei
.
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, numberOfUnitsPerBox <= 1000
1 <= truckSize <= 106
Solution:
Sorting Array:
Algorithm:
- Sort array
boxTypes
such that boxType with max units per box are first in the array. - Start consuming boxes from starting of the array. Reduce truckSize according to the boxes consumed and add units to result
maxUnits
.
class Solution {
public int maximumUnits(int[][] boxTypes, int truckSize) {
Arrays.sort(boxTypes, (a, b) -> b[1] - a[1]);
int maxUnits = 0;
int index = 0;
while(truckSize > 0 && index < boxTypes.length) {
int boxes = boxTypes[index][0];
int unitsPerBox = boxTypes[index][1];
if(boxes > truckSize) {
boxes = truckSize;
}
maxUnits += (boxes * unitsPerBox);
truckSize -= boxes;
index++;
}
return maxUnits;
}
}
Time Complexity: O(n log n) + O(n)
where n
is length of array. This is required for sorting and iterating through array
Space Complexity: O(1)
as we don't need any extra data structure
Creating boxes bucket:
Algorithm:
- As constraint is provided
1 <= boxTypes.length <= 1000
we can create bucket to storenumberOfBoxes
onunitPerBox
. - Start iterating from end of the
bucket
so we take more number of units per box. - On each index reduce the number of units from
truckSize
and add total units.
class Solution {
public int maximumUnits(int[][] boxTypes, int truckSize) {
int[] bucket = new int[1001];
int maxUnits = 0;
for(int[] boxType : boxTypes) {
int boxes = boxType[0];
int unitPerBox = boxType[1];
bucket[unitPerBox] += boxes;
}
for(int i = 1000; i >= 0 && truckSize > 0; i--) {
if(bucket[i] == 0) continue;
int units = Math.min(truckSize, bucket[i]);
truckSize -= units;
maxUnits += (units * i);
}
return maxUnits;
}
}
Time Complexity: O(n) + O(1001) = O(n)
Where n is length of array. we need to iterate through array boxTypes
once and then we need to iterate over bucket
of constant size(hence ignored)
Space Complexity: O(1001) = O(1)
as we need constant extra space for array bucket