Two leaves
Input
count_leaves(TreeNode(1, TreeNode(2), TreeNode(3)))
Output
2
Nodes 2 and 3 are leaves.
Full lesson preview
Count leaf nodes in a binary tree
Count how many leaf nodes (nodes with no children) are present in a binary tree.
Python practice7 minTrees & Binary TreesBeginnerLast updated March 29, 2026
Problem statement
Given the root of a binary tree, return the number of leaf nodes in the tree. A leaf node is a node with no left and no right child. If the tree is empty, return 0.
Implement count_leaves(root) to return the integer count.
Task
Write a function to count the number of leaves in a binary tree.
Examples
Input format
A single argument: root (TreeNode or None).
Output format
An integer: number of leaf nodes.
Constraints
- Tree size up to a few thousand nodes.
- Use recursion or iterative traversal.
Samples
Sample 1
Input
count_leaves(None)
Output
0
Empty tree has zero leaves.