122. 买卖股票的最佳时机②（动态规划，贪心）

解答

def maxProfit(prices):
    n = len(prices)
    if n <= 1:
        return 0
    buy = prices[0]
    max_profit = [0]
    profit = 0
    for i in range(1, n):
        # buy
        if prices[i] < buy:
            profit = max(max_profit)
            buy = prices[i]
        else:
            profit = profit + (prices[i] - buy)
            max_profit.append(profit)
            buy = prices[i]
    return max(max_profit)

2.贪心算法

def maxProfit(prices):
    n = len(prices)
    profit = 0
    for i in range(n-1):
        tmp = prices[i+1]-prices[i]
        if tmp > 0:
            profit += tmp
        else:
            continue
    return profit

空间复杂度更小，O(1)