Update 0042接雨水.md 动态规划和单调栈Python3 版本

problems/0042.接雨水.md

@@ -388,6 +388,44 @@ class Solution:
                 res += res1
         return res
 ```
+动态规划
+```python3
+class Solution:
+    def trap(self, height: List[int]) -> int:
+        leftheight, rightheight = [0]*len(height), [0]*len(height)
+        
+        leftheight[0]=height[0]
+        for i in range(1,len(height)):
+            leftheight[i]=max(leftheight[i-1],height[i])
+        rightheight[-1]=height[-1]
+        for i in range(len(height)-2,-1,-1):
+            rightheight[i]=max(rightheight[i+1],height[i])
+        
+        result = 0
+        for i in range(0,len(height)):
+            summ = min(leftheight[i],rightheight[i])-height[i]
+            result += summ
+        return result
+```
+单调栈
+```python3
+class Solution:
+    def trap(self, height: List[int]) -> int:
+        st =[0]
+        result = 0
+        for i in range(1,len(height)):
+            while st!=[] and height[i]>height[st[-1]]:
+                midh = height[st[-1]]
+                st.pop()
+                if st!=[]:
+                    hright = height[i]
+                    hleft = height[st[-1]]
+                    h = min(hright,hleft)-midh
+                    w = i-st[-1]-1
+                    result+=h*w
+            st.append(i)
+        return result
+```
 
 Go: