add : Best time to buy and sell stock program under GREEDY methods (#10114)

* to add best_time_stock program

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* Update best_time_to_buy_and_sell_stock.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

greedy_methods/best_time_to_buy_and_sell_stock.py

@@ -0,0 +1,42 @@
+"""
+Given a list of stock prices calculate the maximum profit that can be made from a
+single buy and sell of one share of stock.  We only allowed to complete one buy
+transaction and one sell transaction but must buy before we sell.
+
+Example : prices = [7, 1, 5, 3, 6, 4]
+max_profit will return 5 - which is by buying at price 1 and selling at price 6.
+
+This problem can be solved using the concept of "GREEDY ALGORITHM".
+
+We iterate over the price array once, keeping track of the lowest price point
+(buy) and the maximum profit we can get at each point.  The greedy choice at each point
+is to either buy at the current price if it's less than our current buying price, or
+sell at the current price if the profit is more than our current maximum profit.
+"""
+
+
+def max_profit(prices: list[int]) -> int:
+    """
+    >>> max_profit([7, 1, 5, 3, 6, 4])
+    5
+    >>> max_profit([7, 6, 4, 3, 1])
+    0
+    """
+    if not prices:
+        return 0
+
+    min_price = prices[0]
+    max_profit: int = 0
+
+    for price in prices:
+        min_price = min(price, min_price)
+        max_profit = max(price - min_price, max_profit)
+
+    return max_profit
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    print(max_profit([7, 1, 5, 3, 6, 4]))