diff --git a/problems/0121.买卖股票的最佳时机.md b/problems/0121.买卖股票的最佳时机.md
index 63ac5d04..cf17f48d 100644
--- a/problems/0121.买卖股票的最佳时机.md
+++ b/problems/0121.买卖股票的最佳时机.md
@@ -310,6 +310,18 @@ class Solution:
         return dp[(length-1) % 2][1]
 ```
 
+> 动态规划：版本三
+```python
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        length = len(prices)
+        dp0, dp1 = -prices[0], 0 #注意这里只维护两个常量，因为dp0的更新不受dp1的影响
+        for i in range(1, length):
+            dp1 = max(dp1, dp0 + prices[i])
+            dp0 = max(dp0, -prices[i])
+        return dp1
+```
+
 Go:
 > 贪心法：
 ```Go