# Count Complete Tree Nodes LeetCode Solution | Easy Approach Share:

Count Complete Tree Nodes Given the `root` of a complete binary tree, return the number of the nodes in the tree.

According to Wikipedia, every level, except possibly the last, is completely filled in a complete binary tree, 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`.

Design an algorithm that runs in less than `O(n)` time complexity.

Example 1:

```Input: root = [1,2,3,4,5,6]
Output: 6
```

Example 2:

```Input: root = []
Output: 0
```

Example 3:

```Input: root = 
Output: 1
```

Constraints:

• The number of nodes in the tree is in the range `[0, 5 * 104]`.
• `0 <= Node.val <= 5 * 104`
• The tree is guaranteed to be complete.

Time: O(n)
Space: O(h)

### C++

`````` class Solution {
public:
int countNodes(TreeNode* root) {
if (!root)
return 0;
return 1 + countNodes(root->left) + countNodes(root->right);
}
};
``````

### Java

``````
class Solution {
public int countNodes(TreeNode root) {
if (root == null)
return 0;
return 1 + countNodes(root.left) + countNodes(root.right);
}
}
``````

### Python

``````
class Solution:
def countNodes(self, root: Optional[TreeNode]) -> int:
if not root:
return 0
return 1 + self.countNodes(root.left) + self.countNodes(root.right)
``````

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