Count Complete Tree Nodes

#1

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```

#2

The below algorithm uses a simple recursion and counts each node in a given binary tree.

``````func countNodes(root *TreeNode) int {
var count int
helper(root, &count)
return count
}

func helper(root *TreeNode, count *int){
if root==nil{
return
}
helper(root.Left, count)
helper(root.Right, count)
*count++
}
``````

#3

The below code recursively calculates the count without an extra variable.

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