Update 0222.完全二叉树的节点个数.md

problems/0222.完全二叉树的节点个数.md

@@ -393,6 +393,20 @@ class Solution: # 利用完全二叉树特性
             return 2**count-1
         return 1+self.countNodes(root.left)+self.countNodes(root.right)  
 ```
+完全二叉树写法3
+```python
+class Solution: # 利用完全二叉树特性
+    def countNodes(self, root: TreeNode) -> int:
+        if not root: return 0
+        count = 0
+        left = root.left; right = root.right
+        while left and right:
+            count+=1
+            left = left.left; right = right.right
+        if not left and not right: # 如果同时到底说明是满二叉树，反之则不是
+            return (2<<count)-1
+        return 1+self.countNodes(root.left)+self.countNodes(root.right)  
+```
 
 ## Go