diff --git a/include/s0122_best_time_to_buy_and_sell_stock_ii.hpp b/include/s0122_best_time_to_buy_and_sell_stock_ii.hpp
new file mode 100644
index 0000000..14c7bb2
--- /dev/null
+++ b/include/s0122_best_time_to_buy_and_sell_stock_ii.hpp
@@ -0,0 +1,14 @@
+#ifndef S0122_BEST_TIME_TO_BUY_AND_SELL_STOCK_II_HPP
+#define S0122_BEST_TIME_TO_BUY_AND_SELL_STOCK_II_HPP
+
+#include <algorithm>
+#include <vector>
+
+using namespace std;
+
+class S0122 {
+ public:
+  int maxProfit(vector<int>& prices);
+};
+
+#endif
diff --git a/notes/src/SUMMARY.md b/notes/src/SUMMARY.md
index 4763517..62de650 100644
--- a/notes/src/SUMMARY.md
+++ b/notes/src/SUMMARY.md
@@ -57,6 +57,7 @@
 - [基础问题](./dynamic-programming-basic.md)
 - [背包问题](./knapsack.md)
 - [打家劫舍](./house-robber.md)
+- [股票问题](./stock.md)
 
 # STL
 
diff --git a/notes/src/stock.md b/notes/src/stock.md
new file mode 100644
index 0000000..6f31fbc
--- /dev/null
+++ b/notes/src/stock.md
@@ -0,0 +1,18 @@
+# 股票问题
+
+## [122. 买卖股票的最佳时机 II](https://leetcode.cn/problems/best-time-to-buy-and-sell-stock-ii/)
+
+- `dp[i][0]` 表示第 i 天持有股票情况下的资产总额，`dp[i][1]` 表示第 i 天没有持有股票情况下的资产总额。这里的资产不包括股票本身的价值，只包括自身的现金，如果你在第 1 天买入了股票，那么你的资产总额是 `-prices[0]`。
+- 递推公式：
+  - 我们先来讨论 `dp[i][0]`，也就是第 i 天持有股票时的资产，分两种情况
+    - 第 i - 1 天持有股票，那么第 i 天的资产就是 `dp[i - 1][0]`
+    - 第 i - 1 天没持有股票，那么第 i 天的资产就是 `dp[i - 1][1] - prices[i]`
+    - 取这两者的最大值即为第 i 天的最大资产 `dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i])`
+  - 同理 `dp[i][1]` 也分两种情况
+    - 第 i - 1 天持有股票，那么第 i 天的资产就是 `dp[i - 1][0] + prices[0]`
+    - 第 i - 1 天没持有股票，那么第 i 天的资产就是 `dp[i - 1][1]`
+    - 取这两者的最大值即为第 i 天的最大资产 `dp[i][1] = max(dp[i - 1][0] + prices[i], dp[i - 1][1])`
+- 初始化
+  - `dp[0][0] = -prices[0]`
+  - `dp[0][1] = 0`
+- 遍历顺序：从前往后
diff --git a/src/s0122_best_time_to_buy_and_sell_stock_ii.cpp b/src/s0122_best_time_to_buy_and_sell_stock_ii.cpp
new file mode 100644
index 0000000..0770098
--- /dev/null
+++ b/src/s0122_best_time_to_buy_and_sell_stock_ii.cpp
@@ -0,0 +1,12 @@
+#include "s0122_best_time_to_buy_and_sell_stock_ii.hpp"
+
+int S0122::maxProfit(vector<int>& prices) {
+  int len = prices.size();
+  vector<vector<int>> dp(len, vector<int>{0, 0});
+  dp[0][0] = -prices[0];
+  for (int i{1}; i < len; ++i) {
+    dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i]);
+    dp[i][1] = max(dp[i - 1][0] + prices[i], dp[i - 1][1]);
+  }
+  return max(dp[len - 1][1], 0);
+}
diff --git a/tests/s0122_best_time_to_buy_and_sell_stock_ii.cpp b/tests/s0122_best_time_to_buy_and_sell_stock_ii.cpp
new file mode 100644
index 0000000..57f30aa
--- /dev/null
+++ b/tests/s0122_best_time_to_buy_and_sell_stock_ii.cpp
@@ -0,0 +1,17 @@
+#include "s0122_best_time_to_buy_and_sell_stock_ii.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem122, Case1) {
+  vector<int> prices{7, 1, 5, 3, 6, 4};
+  int expected{7};
+  S0122 solution;
+  EXPECT_EQ(solution.maxProfit(prices), expected);
+}
+
+TEST(Problem122, Case2) {
+  vector<int> prices{7, 6, 4, 3, 1};
+  int expected{0};
+  S0122 solution;
+  EXPECT_EQ(solution.maxProfit(prices), expected);
+}