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股票问题是一个动态规划的系列问题，今日安排的题目不多，大家可以慢慢消化。
121. 买卖股票的最佳时机
视频讲解：https://www.bilibili.com/video/BV1Xe4y1u77q
https://programmercarl.com/0121.%E4%B9%B0%E5%8D%96%E8%82%A1%E7%A5%A8%E7%9A%84%E6%9C%80%E4%BD%B3%E6%97%B6%E6%9C%BA.html
Python:
class Solution:def maxProfit(self, prices: List[int]) -> int:n = len(prices)dp = [[0, 0] for _ in range(n)]dp[0][0] = -prices[0]dp[0][1] = 0for i in range(1, n):dp[i][0] = max(dp[i-1][0], -prices[i]) # 持有股票所得现金dp[i][1] = max(dp[i-1][1], prices[i]+dp[i-1][0]) # 不持有股票所得现金return dp[n-1][1]C++:
class Solution {
public:int maxProfit(vector<int>& prices) {int n = prices.size();vector<vector<int>> dp(n, vector<int>(2));dp[0][0] = -prices[0];dp[0][1] = 0;for (int i=1; i<n; i++) {dp[i][0] = max(dp[i-1][0], -prices[i]);dp[i][1] = max(dp[i-1][1], prices[i]+dp[i-1][0]);}return dp[n-1][1];}
};122.买卖股票的最佳时机II
视频讲解：https://www.bilibili.com/video/BV1D24y1Q7Ls
https://programmercarl.com/0122.%E4%B9%B0%E5%8D%96%E8%82%A1%E7%A5%A8%E7%9A%84%E6%9C%80%E4%BD%B3%E6%97%B6%E6%9C%BAII%EF%BC%88%E5%8A%A8%E6%80%81%E8%A7%84%E5%88%92%EF%BC%89.html
Python:
class Solution:def maxProfit(self, prices: List[int]) -> int:n = len(prices)dp = [[0, 0] for _ in range(n)]dp[0][0] = -prices[0]dp[0][1] = 0for i in range(1, n):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[n-1][1]C++:
class Solution {
public:int maxProfit(vector<int>& prices) {int n = prices.size();vector<vector<int>> dp(n, vector<int>(2, 0));dp[0][0] = -prices[0];dp[0][1] = 0;for (int i=1; i<n; i++) {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[n-1][1];}
};