121. 买卖股票的最佳时机
1、动态规划
class Solution:
def maxProfit(self, prices: List[int]) -> int:
# dp[i][0] 代表第 i 天持有股票获取的最大利益
# dp[i][1] 代表第 i 天不持有股票获取的最大利益
dp = [[0] * 2 for _ in range(len(prices))]
dp[0][0] = - prices[0]
dp[0][1] = 0
for i in range(1, len(prices)):
dp[i][0] = max(dp[i-1][0], -prices[i])
dp[i][1] = max(dp[i-1][1], dp[i-1][0] + prices[i])
return dp[-1][1]
2、贪心
class Solution:
def maxProfit(self, prices: List[int]) -> int:
res = 0
low = prices[0]
for i in range(1, len(prices)):
low = min(low, prices[i])
res = max(res, prices[i] - low)
return res
3、动态规划优化
class Solution:
def maxProfit(self, prices: List[int]) -> int:
dp0, dp1 = - prices[0], 0
for i in range(1, len(prices)):
dp1 = max(dp1, dp0 + prices[i])
dp0 = max(dp0, -prices[i])
return dp1
122.买卖股票的最佳时机II
1、动态规划
class Solution:
def maxProfit(self, prices: List[int]) -> int:
# dp[i][0] 不持有股票，dp[i][1] 持有股票
dp = [[0] * 2 for _ in range(len(prices))]
dp[0][0] = 0
dp[0][1] = - prices[0]
for i in range(1, len(prices)):
dp[i][0] = max(dp[i-1][0], dp[i-1][1] + prices[i])
dp[i][1] = max(dp[i-1][1], dp[i-1][0] - prices[i])
return dp[-1][0]