Create 222_Count_Complete_Tree_Nodes.md

Author: koji

222_Count_Complete_Tree_Nodes.md

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+## 222. Count Complete Tree Nodes
+
+```
+Given a complete binary tree, count the number of nodes.
+
+Note:
+
+Definition of a complete binary tree from Wikipedia:
+In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
+
+Example:
+
+Input: 
+ 1
+ / \
+ 2 3
+ / \ /
+4 5 6
+
+Output: 6
+
+```
+
+
+```python
+class Solution:
+ def countNodes(self, root: TreeNode) -> int:
+ if not root: return 0
+ # check depth
+ ld = self.check_depth(root, True)
+ rd = self.check_depth(root, False)
+ # print(ld)
+ # print(rd)
+ if ld == rd:
+ return int(math.pow(2, ld)-1)
+ return int(1 + self.countNodes(root.left) + self.countNodes(root.right))
+ 
+ def check_depth(self, root, lr):
+ if not root: return 0
+ if lr:
+ d = self.check_depth(root.left, lr)
+ else:
+ d = self.check_depth(root.right, lr)
+
+ return d + 1
+```
+
+```
+Runtime: 64 ms, faster than 98.98% of Python3 online submissions for Count Complete Tree Nodes.
+Memory Usage: 21.3 MB, less than 100.00% of Python3 online submissions for Count Complete Tree Nodes.
+
+```