LC 309. Best Time to Buy and Sell Stock with Cooldown

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Description

Say you have an array for which the ith element is the price of a given stock on day i.
Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times) with the following restrictions:
You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day)

Example:
Input: [1,2,3,0,2]
Output: 3
Explanation: transactions = [buy, sell, cooldown, buy, sell]

Solution

ik0: time i, after k transactions, we have stock
ik1: time i, after k transactions, we don’t have stock

Because there is a cooldown, we should store the ik0 before and use it to update ik1 after this round.

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class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        ik0, ik1, before = 0, -float('inf'), 0
        for p in prices:
            tep = ik0
            ik0 = max(ik0, ik1 + p)
            ik1 = max(ik1, before - p)
            before = tep
        return ik0
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