0941.有效的山脉数组 python3 更新双指针方法

0941.有效的山脉数组 python3 从原方法更新到双指针方法

problems/0941.有效的山脉数组.md

@@ -106,22 +106,15 @@ class Solution {
 ```python
 class Solution:
     def validMountainArray(self, arr: List[int]) -> bool:
-        if len(arr) < 3 :
-            return False
-
-        i = 1
-        flagIncrease = False # 上升
-        flagDecrease = False # 下降
-
-        while i < len(arr) and arr[i-1] < arr[i]:
-            flagIncrease = True
-            i += 1
-
-        while i < len(arr) and arr[i-1] > arr[i]:
-            flagDecrease = True
-            i += 1
-
-        return i == len(arr) and flagIncrease and flagDecrease
+        left, right = 0, len(arr)-1
+        
+        while left < len(arr)-1 and arr[left+1] > arr[left]:
+            left += 1
+        
+        while right > 0 and arr[right-1] > arr[right]:
+            right -= 1
+        
+        return left == right and right != 0 and left != len(arr)-1
 
 ```