buyAndSellStock.py

"""
You are given an array prices where prices[i] is the price of a given stock on the ith day.

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

 
Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.

"""



class Solution:
    def maxProfit(self, arr: List[int]) -> int:
        minSoFar=float('inf')
        maxProfit=0
        for i in range(len(arr)):
            minSoFar=min(minSoFar,arr[i])
            maxProfit=max(maxProfit,arr[i]-minSoFar)
        return maxProfit