Lintcode:买卖股票的最佳时机

class Solution:
"""
@param prices: Given an integer array
@return: Maximum profit
"""
def maxProfit(self, prices):
# write your code here
if(len(prices)==0):
return 0
lowest_price = prices[0]
ans = 0
for i in range(len(prices)):
ans = max(ans, prices[i]-lowest_price)
lowest_price = min(prices[i], lowest_price)
return ans