1475. Final Prices With a Special Discount in a Shop

Problem Link

Description

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You are given an integer array prices where prices[i] is the price of the ith item in a shop.

There is a special discount for items in the shop. If you buy the ith item, then you will receive a discount equivalent to prices[j] where j is the minimum index such that j > i and prices[j] <= prices[i]. Otherwise, you will not receive any discount at all.

Return an integer array answer where answer[i] is the final price you will pay for the ith item of the shop, considering the special discount.

 

Example 1:

Input: prices = [8,4,6,2,3]
Output: [4,2,4,2,3]
Explanation: 
For item 0 with price[0]=8 you will receive a discount equivalent to prices[1]=4, therefore, the final price you will pay is 8 - 4 = 4.
For item 1 with price[1]=4 you will receive a discount equivalent to prices[3]=2, therefore, the final price you will pay is 4 - 2 = 2.
For item 2 with price[2]=6 you will receive a discount equivalent to prices[3]=2, therefore, the final price you will pay is 6 - 2 = 4.
For items 3 and 4 you will not receive any discount at all.

Example 2:

Input: prices = [1,2,3,4,5]
Output: [1,2,3,4,5]
Explanation: In this case, for all items, you will not receive any discount at all.

Example 3:

Input: prices = [10,1,1,6]
Output: [9,0,1,6]

 

Constraints:

• 1 <= prices.length <= 500
• 1 <= prices[i] <= 1000

Solution

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Python3

class Solution:
    def finalPrices(self, prices: List[int]) -> List[int]:
        N = len(prices)
        nextSmaller = [-1] * N
        stack = []
 
        for i, x in enumerate(prices):
            while stack and x <= prices[stack[-1]]:
                nextSmaller[stack.pop()] = i
            
            stack.append(i)
 
        for i in range(N):
            if nextSmaller[i] != -1:
                prices[i] -= prices[nextSmaller[i]]
        
        return prices