Number of Visible Nodes
There is a binary tree with N nodes. You are viewing the tree from its left side and can see only the leftmost nodes at each level. Return the number of visible nodes.
Note: You can see only the leftmost nodes, but that doesn't mean they have to be left nodes. The leftmost node at a level could be a right node.
Signature
int visibleNodes(Node root) {
Input
The root node of a tree, where the number of nodes is between 1 and 1000, and the value of each node is between 0 and 1,000,000,000
Output
An int representing the number of visible nodes.
Example
8 <------ root
/
3 10
/ \
1 6 14
/ \ /
4 7 13
output = 4

Since we are basically counting how many levels are in the tree:

def visible_nodes(root):
    if root is None:
      return 0
    else:
      return max(visible_nodes(root.left),visible_nodes(root.right)) + 1