Question:Given the root pointer to a binary tree, find the number of leaves.

Input:Sample Tree (Pointer to node 1 is given). Find the number of leaves.

Output:Number of leaves = 4

*According to the definition, the set of all nodes whose both left and right child are null, are known as leaf nodes.*

In the above example, we have the nodes – 7, 9, 5, 4 as the leaf nodes.

We can perform a level order traversal and count the number of nodes, who have their right child and left child as null. Return the count in the end.

#include<stdio.h> #include<malloc.h> struct binaryTreeNode{ int data; struct binaryTreeNode * left; struct binaryTreeNode * right; }; int numberOfLeaves(struct binaryTreeNode * root) { // Level order traversal struct binaryTreeNode * temp = NULL; struct queue * Q = NULL; // Maintain a count int count = 0; if(root == NULL) return 0; Q = enQueue(Q, root); while(!isQueueEmpty(Q)) { temp = Q -> front -> data; // Now check if the node is a leaf node if(temp -> left == NULL && temp -> right == NULL) { // This means a leaf node count++; } Q = deQueue(Q); if(temp -> left) Q = enQueue(Q, temp -> left); if(temp -> right) Q = enQueue(Q, temp -> right); } // Delete the queue free(Q); // Now return the count return count; }

*Time Complexity:-* O(n)

*Space Complexity:-* O(n)

**Ideone link for the sample program:-** http://ideone.com/umTait