1705_Maximum_Number_of_EatenApples.py

"""
1705. Maximum Number of Eaten Apples
There is a special kind of apple tree that grows apples every day for n days. On the ith day, the tree grows apples[i] apples that will rot after days[i] days, that is on day i + days[i] the apples will be rotten and cannot be eaten. On some days, the apple tree does not grow any apples, which are denoted by apples[i] == 0 and days[i] == 0.

You decided to eat at most one apple a day (to keep the doctors away). Note that you can keep eating after the first n days.

Given two integer arrays days and apples of length n, return the maximum number of apples you can eat.

 

Example 1:

Input: apples = [1,2,3,5,2], days = [3,2,1,4,2]
Output: 7
Explanation: You can eat 7 apples:
- On the first day, you eat an apple that grew on the first day.
- On the second day, you eat an apple that grew on the second day.
- On the third day, you eat an apple that grew on the second day. After this day, the apples that grew on the third day rot.
- On the fourth to the seventh days, you eat apples that grew on the fourth day.
Example 2:

Input: apples = [3,0,0,0,0,2], days = [3,0,0,0,0,2]
Output: 5
Explanation: You can eat 5 apples:
- On the first to the third day you eat apples that grew on the first day.
- Do nothing on the fouth and fifth days.
- On the sixth and seventh days you eat apples that grew on the sixth day.
 

Constraints:

n == apples.length == days.length
1 <= n <= 2 * 104
0 <= apples[i], days[i] <= 2 * 104
days[i] = 0 if and only if apples[i] = 0.

"""
class Solution:
    def eatenApples(self, apples: List[int], days: List[int]) -> int:
        t = 0
        total = 0
        heap = [(days[0], apples[0])]
        while heap or t <len(days):
            if heap:
                # pop all insignificant items
                while heap and heap[0][0] <= t:
                    heapq.heappop(heap)
                
                if heap:
                    day,apple = heapq.heappop(heap)
                    # If there are more apples to eat reinsert
                    if apple > 1 and day > t+1:
                        heapq.heappush(heap, (day, apple-1))
                    
                    # keep track of the apples eaten
                    total += 1
            t += 1
            # Load the heap for the next iteration
            if t < len(days):
                if apples[t] > 0:
                    heapq.heappush(heap, (t+days[t], apples[t]))      
        return total