solve Best Time to Buy and Sell Stock

Author: saubhik

problems/best_time_to_buy_and_sell_stock.py

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+from typing import List
+
+
+class Solution:
+    # Straight Forward DP.
+    #
+    # Time: O(n). One Pass.
+    # Space: O(1) additional space.
+    #
+    #              [ 7,    1, 5, 3, 6, 4]
+    # min_cost  :  inf,  inf, 1, 1, 1, 1
+    # profit_i  : -inf, -inf, 4, 2, 5, 3
+    # Max of profit_i is 5.
+    def maxProfit(self, prices: List[int]) -> int:
+        min_cost_before_i = float("inf")
+        max_profit = 0
+        for price in prices:
+            max_profit = max(max_profit, price - min_cost_before_i)
+            min_cost_before_i = min(min_cost_before_i, price)
+        return max_profit

tests/test_best_time_to_buy_and_sell_stock.py

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+import unittest
+
+from best_time_to_buy_and_sell_stock import Solution
+
+
+class TestBestTimeToBuyAndSellStock(unittest.TestCase):
+    def test_example_1(self):
+        assert Solution().maxProfit(prices=[7, 1, 5, 3, 6, 4]) == 5
+
+    def test_example_2(self):
+        assert Solution().maxProfit(prices=[]) == 0
+
+    def test_example_3(self):
+        assert Solution().maxProfit(prices=[7, 6, 4, 3, 1]) == 0