Program to find maximum number of eaten apples in Python

Suppose we have two arrays called days and apples of same length n. There is a special kind of apple tree that grows apples every day for n consecutive days. On the ith day, it grows apples[i] number of apples and that will rot after days[i] days, so we can say it like that on day i + days[i] the apples will be rotten and cannot be eaten. On some days. If apples[i] = 0, and days[i] = 0, then it indicates on day i, the apple tree is not growing any apple. We can take at most one apple a day. (We can keep eating after the first n days). Here we have to find the maximum number of apples we can eat.

So, if the input is like apples = [1,2,3,5,2] days = [3,2,1,4,2], then the output will be 7 because −

• On day 1, we eat an apple that grew on the first day.

• On day 2, we eat an apple that grew on the second day.

• On day 3, we eat an apple that grew on the second day. But after this day, the apples that grew on the third day will rot.

• On days from 4 to 7, we eat apples that grew on the fourth day.

To solve this, we will follow these steps −

• minheap := a new empty heap
• day := 0, res := 0
• for i in range 0 to size of apples - 1, do
  • day := i
  • while minheap is not empty and rot value of top of minheap − day, do
    • remove top element from minheap
  • nbrApple := apples[i]
  • expiration := i + days[i]-1
  • if nbrApple > 0, then
    • insert (expiration, nbrApple) pair into minheap
  • if minheap is not empty, then
    • (date, apple) := top element of minheap and remove it from heap
    • res := res + 1
    • if apple > 1, then
      • insert (date, apple-1) pair into minheap
• while minheap is not empty, do
  • day := day + 1
  • while minheap is not empty and rot value of top of minheap < day, do
    • remove top element from minheap
  • if minheap is empty, then
    • come out from loop
  • (date, apple) := top of minheap and remove it from heap
  • res := res + 1
  • if apple > 1, then
    • insert (date, apple-1) pair into minheap
• return res

Example

Let us see the following implementation to get better understanding −

import heapq
def solve(apples, days):
   minheap = []
   heapq.heapify(minheap)
   day = 0
   res = 0
   for i in range(len(apples)):
      day = i

      while minheap and minheap[0][0] < day:
         heapq.heappop(minheap)

      nbrApple = apples[i]
      expiration = i + days[i]-1

      if nbrApple > 0:
         heapq.heappush(minheap, (expiration, nbrApple))

      if minheap:
         date, apple = heapq.heappop(minheap)
         res += 1
         if apple > 1:
            heapq.heappush(minheap, (date, apple-1))

   while minheap:
      day += 1
      while minheap and minheap[0][0] < day:
         heapq.heappop(minheap)
      if minheap == []:
         break
      date, apple = heapq.heappop(minheap)
      res += 1
      if apple > 1:
         heapq.heappush(minheap, (date, apple-1))

   return res

apples = [1,2,3,5,2]
days = [3,2,1,4,2]
print(solve(apples, days))

Input

[1,2,3,5,2],[3,2,1,4,2]

Output

7