2020-04-13 Day 51 Leetcode: 121.

class Solution:
    def maxProfit(self, prices: List[int]) -> int:
        if not prices:
            return 0
        pre_min=[prices[0]]
        for i in range(1,len(prices)):
            pre_min.append(min(prices[:i]))
        
        profit=[0]
        for i in range(1,len(prices)):
            profit.append(prices[i]-pre_min[i])
        return max(profit)