O(n) time and O(1) using Greedy Approach.

Author: 149ps

714. Best Time to Buy and Sell Stock with Transaction Fee/714. Best Time to Buy and Sell Stock with Transaction Fee.py

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+"""
+Your are given an array of integers prices, for which the i-th element is the price of a given stock on day i; and a non-negative integer fee representing a transaction fee.
+
+You may complete as many transactions as you like, but you need to pay the transaction fee for each transaction. You may not buy more than 1 share of a stock at a time (ie. you must sell the stock share before you buy again.)
+
+Return the maximum profit you can make.
+
+Example 1:
+Input: prices = [1, 3, 2, 8, 4, 9], fee = 2
+Output: 8
+Explanation: The maximum profit can be achieved by:
+Buying at prices[0] = 1
+Selling at prices[3] = 8
+Buying at prices[4] = 4
+Selling at prices[5] = 9
+The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8.
+Note:
+
+0 < prices.length <= 50000.
+0 < prices[i] < 50000.
+0 <= fee < 50000.
+"""
+class Solution:
+    def maxProfit(self, prices: List[int], fee: int) -> int:
+        min_stock = prices[0]
+        max_profit = 0
+        for i in range(1,len(prices)):
+            if prices[i] < min_stock:
+                min_stock = prices[i]
+            elif prices[i] > min_stock + fee:
+                max_profit += prices[i] - min_stock - fee
+                min_stock = prices[i] - fee
+        return max_profit