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# 0121 Best Time to Buy and Sell Stock

Solved at: 2022-07-13

## Question​

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.

## Solution​

class Solution:    def maxProfit(self, prices: List[int]) -> int:        if not prices:            return 0        minv = prices[0]        profit = 0        for i, price in enumerate(prices):            if price < minv:                minv = price            else:                if profit < prices[i] - minv:                    profit = prices[i] - minv        return profit

I had to get a hint to keep the minimum value so far.

• Time Complexity: $O(n)$
• Space Complexity: $O(1)$

## Results​

### Runtime​

• 1698 ms, faster than 38.38% of Python3 online submissions for Best Time to Buy and Sell Stock.

### Memory Usage​

• 25 MB, less than 37.97% of Python3 online submissions for Best Time to Buy and Sell Stock.