C++ Program to Check Whether a given Binary Tree is a Full Binary Tree or not

Given a Binary Tree, the task is to check whether it is a Full Binary Tree or not. A Binary Tree is said to be a Full Binary Tree if every node has zero or two children.

For Example




Explanation: Every node except the leaf node has two children, so it is a full binary tree.




Explanation: Node 2 has only one child, so it is not a full binary tree.

Approach to Solve this Problem

To check whether a given binary tree is full or not, we can check recursively for the left subtree and right subtree.

  • Input a given Binary Tree having nodes and its children.
  • A Boolean function isFullBinaryTree(Node*root) takes the root node as the input and returns True if it is full binary tree, otherwise false.
  • In the base condition, if the root node is NULL or empty, then return True.
  • If the left subtree and the right subtree is NULL or empty, then return True.
  • Now let us check recursively for each of the left subtree and right subtree and return the output.


Live Demo

using namespace std;
struct treenode {
   int data;
   treenode * left;
   treenode * right;
struct treenode * createNode(int d) {
   struct treenode * root = new treenode;
   root -> data = d;
   root -> left = NULL;
   root -> right = NULL;
   return root;
bool isFullBinaryTree(struct treenode * root) {
   if (root == NULL) {
      return true;
   if (root -> left == NULL and root -> right == NULL) {
      return true;
   } else if (root -> left and root -> right) {
      return (isFullBinaryTree(root -> left) and isFullBinaryTree(root -> right));
   return false;
int main() {
   struct treenode * root = NULL;
   root = createNode(1);
   root -> left = createNode(2);
   root -> right = createNode(3);
   root -> left -> right = createNode(4);
   root -> left -> left = createNode(5);
   root -> right -> left = createNode(6);
   if (isFullBinaryTree(root)) {
      cout << "1" << endl;
   } else {
      cout << "0" << endl;
   return 0;

Running the above code will generate the output as,



Explanation: Since all the leaf nodes in the given binary tree do not have children nodes, it is not a Full Binary Tree. So, we get the output as 0.