feat: 更加优雅的Python Code

Author: azl397985856

problems/42.trapping-rain-water.md

@@ -96,26 +96,16 @@ var trap = function(height) {
 Python Code:
 
 ```python
-
 class Solution:
-    def trap(self, height: List[int]) -> int:
-        maxLeft, maxRight, volum = 0, 0, 0
-        maxLeftStack, maxRightStack = [], []
-        for h in height:
-            if h > maxLeft:
-                maxLeftStack.append(h)
-                maxLeft = h
-            else:
-                maxLeftStack.append(maxLeft)
-        for h in height[::-1]:
-            if h > maxRight:
-                maxRightStack.append(h)
-                maxRight = h
-            else:
-                maxRightStack.append(maxRight)
-        maxRightStack = maxRightStack[::-1]
-        for i in range(1, len(height) - 1):
-            minSide = min(maxLeftStack[i], maxRightStack[i])
-            volum += minSide - height[i]
-        return volum      
+    def trap(self, heights: List[int]) -> int:
+        n = len(heights)
+        l, r = [0] * (n + 1), [0] * (n + 1)
+        ans = 0
+        for i in range(1, len(heights) + 1):
+            l[i] = max(l[i - 1], heights[i - 1])
+        for i in range(len(heights) - 1, 0, -1):
+            r[i] = max(r[i + 1], heights[i])
+        for i in range(len(heights)):
+            ans += max(0, min(l[i + 1], r[i]) - heights[i])
+        return ans     
 ```