Best Time To Buy And Sell Stock

121. Best Time To Buy And Sell Stock

Difficulty: Easy

Related Topics: Array, Two Pointers, Dynamic Programming

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.

Code:

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        l, r = 0, 1
        res = 0

        while r < len(prices):
            if prices[l] < prices[r]:
                res = max(res, prices[r] - prices[l])
                # r += 1  
            else:
                # l += 1
                # r = l + 1
                l = r   # Shift left pointer to right pointer in order to avoid duplicate calculation
            r += 1

        return res