feat: count-complete-tree-nodes

Author: junbinding

Diff for: bt.count-complete-tree-nodes.py

@@ -0,0 +1,20 @@
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+class Solution:
+    """
+    222. 完全二叉树的节点个数
+    https://leetcode-cn.com/problems/count-complete-tree-nodes
+    说明：
+    完全二叉树的定义如下：在完全二叉树中，除了最底层节点可能没填满外，其余每层节点数都达到最大值，
+    并且最下面一层的节点都集中在该层最左边的若干位置。若最底层为第 h 层，则该层包含 1~ 2h 个节点。
+    """
+    def countNodes(self, root: TreeNode) -> int:
+        if not root:
+            return 0
+
+        return 1 + self.countNodes(root.left) + self.countNodes(root.right)