<p>You are assigned to put some amount of boxes onto <strong>one truck</strong>. You are given a 2D array <code>boxTypes</code>, where <code>boxTypes[i] = [numberOfBoxes<sub>i</sub>, numberOfUnitsPerBox<sub>i</sub>]</code>:</p>

<ul>
	<li><code>numberOfBoxes<sub>i</sub></code> is the number of boxes of type <code>i</code>.</li>
	<li><code>numberOfUnitsPerBox<sub>i</sub></code><sub> </sub>is the number of units in each box of the type <code>i</code>.</li>
</ul>

<p>You are also given an integer <code>truckSize</code>, which is the <strong>maximum</strong> number of <strong>boxes</strong> that can be put on the truck. You can choose any boxes to put on the truck as long as the number&nbsp;of boxes does not exceed <code>truckSize</code>.</p>

<p>Return <em>the <strong>maximum</strong> total number of <strong>units</strong> that can be put on the truck.</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> boxTypes = [[1,3],[2,2],[3,1]], truckSize = 4
<strong>Output:</strong> 8
<strong>Explanation:</strong> 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.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> boxTypes = [[5,10],[2,5],[4,7],[3,9]], truckSize = 10
<strong>Output:</strong> 91
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= boxTypes.length &lt;= 1000</code></li>
	<li><code>1 &lt;= numberOfBoxes<sub>i</sub>, numberOfUnitsPerBox<sub>i</sub> &lt;= 1000</code></li>
	<li><code>1 &lt;= truckSize &lt;= 10<sup>6</sup></code></li>
</ul>

"""
1. the largest amount will be taking as many boxes of the largest units as possible and moving down the line, making this a greedy problem
2. we sort the box types by the units
3. we go through the largest and add up the sum and subtract from the truck size
4. keep going until we reach truck size of 0 and return the sum

"""
class Solution:
    def maximumUnits(self, boxTypes: List[List[int]], truckSize: int) -> int:
        boxTypes.sort(key = lambda x : x[1], reverse=True)
        box_sum = 0
        for boxes,units in boxTypes:
            for box in range(boxes):
                box_sum += units
                truckSize -= 1
                if truckSize == 0:
                    return box_sum
        return box_sum
545