add solution: best-time-to-buy-and-sell-stock

Author: dusunax

best-time-to-buy-and-sell-stock/dusunax.py

@@ -0,0 +1,31 @@
+'''
+# 121. Best Time to Buy and Sell Stock
+
+use **bottom-up dynamic programming** to solve the problem.
+
+## Time and Space Complexity
+```
+TC: O(n)
+SC: O(1)
+```
+
+## TC is O(n):
+- iterating through the list just once to find the maximum profit. = O(n)
+
+## SC is O(1):
+- using two variables to store the minimum price and maximum profit. = O(1)
+'''
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        if len(prices) == 1:
+            return 0
+        
+        lowest_price = prices[0] # SC: O(1)
+        max_profit = 0 # SC: O(1)
+        
+        for price in prices: # TC: O(n)
+            lowest_price = min(price, lowest_price)
+            curr_profit = price - lowest_price
+            max_profit = max(curr_profit, max_profit)
+        
+        return max_profit