Count frequency of K in given Binary Tree
Last Updated :
23 Jul, 2025
Given a binary tree of N nodes. Count the frequency of an integer K in the binary tree.
Examples:
Input: N = 7, K = 2
1
/ \
2 3
/ \ / \
4 2 2 5
Output: 3
Explanation: 2 occurs 3 times in the tree.
Input: N = 6, K = 5
1
/ \
4 5
/ \ / \
5 6 2 4
Output: 2
Explanation: 5 occurs 2 times in the tree.
Approach: The solution to the problem is based on the traversal of the given binary tree. Follow the steps as shown below:
Below is the implementation of the above approach.
C++
// C++ code to implement the approach
#include <bits/stdc++.h>
using namespace std;
// Structure of a tree node
struct Node {
int data;
struct Node* left;
struct Node* right;
Node(int data)
{
this->data = data;
left = right = NULL;
}
};
// Function for inorder tree traversal
int countOccurrence(struct Node* root, int K)
{
stack<Node*> s;
Node* curr = root;
// Variable for counting frequency of K
int count = 0;
while (curr != NULL || s.empty() == false) {
// Reach the left most Node
// of the curr Node
while (curr != NULL) {
// Place pointer to a tree node
// on the stack before
// traversing the node's
// left subtree
s.push(curr);
curr = curr->left;
}
// Current must be NULL at this point
curr = s.top();
s.pop();
// Increment count if element = K
if (curr->data == K)
count++;
// Traverse the right subtree
curr = curr->right;
}
return count;
}
// Driver code
int main()
{
// Binary tree as shown in example
struct Node* root = new Node(1);
root->left = new Node(2);
root->right = new Node(2);
root->left->left = new Node(4);
root->left->right = new Node(2);
int K = 2;
// Function call
int ans = countOccurrence(root, K);
cout << ans << endl;
return 0;
}
// JAVA code to implement the approach
import java.util.*;
// Structure of a tree node
class Node {
int data;
Node left;
Node right;
Node(int data)
{
this.data = data;
left = right = null;
}
}
class GFG {
// Function for inorder tree traversal
public static int countOccurrence(Node root, int K)
{
Stack<Node> s = new Stack<Node>();
Node curr = root;
// Variable for counting frequency of K
int count = 0;
while (curr != null || s.empty() == false) {
// Reach the left most Node
// of the curr Node
while (curr != null) {
// Place pointer to a tree node
// on the stack before
// traversing the node's
// left subtree
s.push(curr);
curr = curr.left;
}
// Current must be NULL at this point
curr = s.peek();
s.pop();
// Increment count if element = K
if (curr.data == K)
count++;
// Traverse the right subtree
curr = curr.right;
}
return count;
}
// Driver code
public static void main(String[] args)
{
// Binary tree as shown in example
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
int K = 2;
// Function call
int ans = countOccurrence(root, K);
System.out.println(ans);
}
}
// This code is contributed by Taranpreet
# Python code for the above approach
# Structure of a tree node
class Node:
def __init__(self,d):
self.data = d
self.left = None
self.right = None
# Function for inorder tree traversal
def countOccurrence(root, K):
s = []
curr = root
# Variable for counting frequency of K
count = 0
while (curr != None or len(s) != 0):
# Reach the left most Node
# of the curr Node
while (curr != None):
# Place pointer to a tree node
# on the stack before
# traversing the node's
# left subtree
s.append(curr)
curr = curr.left
# Current must be None at this point
curr = s[len(s) - 1]
s.pop()
# Increment count if element = K
if (curr.data == K):
count += 1
# Traverse the right subtree
curr = curr.right
return count
# Driver code
# Binary tree as shown in example
root = Node(1)
root.left = Node(2)
root.right = Node(2)
root.left.left = Node(4)
root.left.right = Node(2)
K = 2
# Function call
ans = countOccurrence(root, K)
print(ans)
# This code is contributed by shinjanpatra
// C# code to implement the approach
using System;
using System.Collections.Generic;
// Structure of a tree node
public class Node {
public int data;
public Node left;
public Node right;
public Node(int data)
{
this.data = data;
left = right = null;
}
}
class GFG {
// Function for inorder tree traversal
public static int countOccurrence(Node root, int K)
{
Stack<Node> s = new Stack<Node> ();
Node curr = root;
// Variable for counting frequency of K
int count = 0;
while (curr != null || s.Count!=0) {
// Reach the left most Node
// of the curr Node
while (curr != null) {
// Place pointer to a tree node
// on the stack before
// traversing the node's
// left subtree
s.Push(curr);
curr = curr.left;
}
// Current must be NULL at this point
curr = s.Peek();
s.Pop();
// Increment count if element = K
if (curr.data == K)
count++;
// Traverse the right subtree
curr = curr.right;
}
return count;
}
// Driver Code
public static void Main () {
// Build a tree
// Binary tree as shown in example
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
int K = 2;
// Function call
int ans = countOccurrence(root, K);
Console.WriteLine(ans);
}
}
// This code is contributed by jana_sayantan.
<script>
// JavaScript code for the above approach
// Structure of a tree node
class Node {
constructor(d) {
this.data = d;
this.left = null;
this.right = null;
}
};
// Function for inorder tree traversal
function countOccurrence(root, K) {
let s = [];
let curr = root;
// Variable for counting frequency of K
let count = 0;
while (curr != null || s.length != 0) {
// Reach the left most Node
// of the curr Node
while (curr != null) {
// Place pointer to a tree node
// on the stack before
// traversing the node's
// left subtree
s.push(curr);
curr = curr.left;
}
// Current must be null at this point
curr = s[s.length - 1];
s.pop();
// Increment count if element = K
if (curr.data == K)
count++;
// Traverse the right subtree
curr = curr.right;
}
return count;
}
// Driver code
// Binary tree as shown in example
let root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
let K = 2;
// Function call
let ans = countOccurrence(root, K);
document.write(ans + '<br>')
// This code is contributed by Potta Lokesh
</script>
Time Complexity: O(N)
Auxiliary Space: O(N)
Another Approach(using Recursion):
follow the below steps to solve the given problem recursively:
1) traverse the given binary tree in preorder fashion and keep track to count at each node
2) if the current node value is equal to given value(K) then increment k
3) recursively call for left and right subtree.
4) print count answer.
Below is the implementation of above approach:
C++
// c++ program to count frequency of k
// in given binary tree
#include<bits/stdc++.h>
using namespace std;
// Structure of a tree node
struct Node {
int data;
struct Node* left;
struct Node* right;
Node(int data)
{
this->data = data;
left = right = NULL;
}
};
// Function for preorder tree traversal recursively
void countOccurrence(Node* root, int K, int &count){
if(root == NULL) return;
if(root->data == K) count++;
countOccurrence(root->left, K, count);
countOccurrence(root->right, K, count);
}
// Driver code
int main()
{
// Binary tree as shown in example
struct Node* root = new Node(1);
root->left = new Node(2);
root->right = new Node(2);
root->left->left = new Node(4);
root->left->right = new Node(2);
int K = 2;
int ans = 0;
// Function call
countOccurrence(root, K, ans);
cout << ans << endl;
return 0;
}
// this code is contributed by Yash Agarwal(yashagarwal2852002)
/*package whatever //do not write package name here */
import java.io.*;
// Java program to count frequency of k
// in given binary tree
// structure of a tree node
class Node {
int data;
Node left;
Node right;
Node(int data)
{
this.data = data;
this.left = null;
this.right = null;
}
}
class GFG {
static int count = 0;
public static void countOccurrence(Node root, int k)
{
if (root == null)
return;
if (root.data == k)
count++;
countOccurrence(root.left, k);
countOccurrence(root.right, k);
}
// function topreorder tree traversal recursively
public static void main(String[] args)
{
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
int k = 2;
int ans = 0;
countOccurrence(root, k);
System.out.println(count);
}
}
// This code is contributed by anskalyan3.
# Python program to count frequency of k
# in given binary tree
# structure of tree node
class Node:
def __init__(self,key):
self.data = key
self.left = None
self.right = None
# function to preorder tree traversal recursively
count = 0
def countOccurrence(root, K):
if(root is None):
return
if(root.data == K):
global count
count = count + 1
countOccurrence(root.left, K)
countOccurrence(root.right, K)
# driver code
# binary tree as shown in example
root = Node(1)
root.left = Node(2)
root.right = Node(2)
root.left.left = Node(4)
root.left.right = Node(2)
K = 2
# function call
countOccurrence(root, K)
print(count)
// C# program to count frequency of k
// in given binary tree
using System;
using System.Collections.Generic;
class Gfg
{
static int count = 0;
// Structure of a tree node
class Node {
public int data;
public Node left;
public Node right;
public Node(int data)
{
this.data = data;
left = right = null;
}
}
// Function for preorder tree traversal recursively
static void countOccurrence(Node root, int K)
{
if(root == null)
return;
if(root.data == K)
count++;
countOccurrence(root.left, K);
countOccurrence(root.right, K);
}
// Driver code
public static void Main(string[] args)
{
// Binary tree as shown in example
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
int K = 2;
// Function call
countOccurrence(root, K);
Console.Write(count);
}
}
// This code is contributed by ratiagrawal.
// Javascript program to count frequency of k
// in given binary tree
// structure of a tree node
class Node{
constructor(data){
this.data = data;
this.left = null;
this.right = null;
}
}
// function topreorder tree traversal recursively
let count = 0;
function countOccurrence(root, K){
if(root == null) return;
if(root.data == K) count++;
countOccurrence(root.left, K);
countOccurrence(root.right, K);
}
// driver code
// binary tree as shown in example
let root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
let K = 2;
// function call
countOccurrence(root, K);
console.log(count);
// THIS CODE IS CONTRIBUTED BY KIRTI AGARWAL(KIRITAGARWAL23121999)
Time Complexity: O(N) where N is the number of nodes in given binary tree.
Auxiliary Space: O(h) where h is the height of the given tree due to recursion.
Another Iterative and Easiest Approach(Using Level Order Traversal with Queue):
Follow the below steps to solve the given problem:
- Perform level order traversal using Queue data structure.
- At each node in traversal check if it is equal to the given integer k then increment the count variable which is initialized by 0 in starting the level order traversal.
- Simply return the value of count variable.
Below is the implementation of above approach:
C++
// c++ program to count frequency of k
// in given binary tree
#include<bits/stdc++.h>
using namespace std;
// Structure of a tree node
struct Node {
int data;
struct Node* left;
struct Node* right;
Node(int data)
{
this->data = data;
left = right = NULL;
}
};
// Function for preorder tree traversal recursively
void countOccurrence(Node* root, int K, int &count){
// initialize queue for level order traversal
queue<Node*> q;
q.push(root);
while(!q.empty()){
Node* front_node = q.front();
q.pop();
if(front_node->data == K) count++;
if(front_node->left) q.push(front_node->left);
if(front_node->right) q.push(front_node->right);
}
}
// Driver code
int main()
{
// Binary tree as shown in example
struct Node* root = new Node(1);
root->left = new Node(2);
root->right = new Node(2);
root->left->left = new Node(4);
root->left->right = new Node(2);
int K = 2;
int ans = 0;
// Function call
countOccurrence(root, K, ans);
cout << ans << endl;
return 0;
}
// this code is contributed by Kirti Agarwal(kirtiagarwal23121999)
import java.util.LinkedList;
import java.util.Queue;
// Structure of a tree node
class Node {
int data;
Node left;
Node right;
Node(int data) {
this.data = data;
left = right = null;
}
}
public class Main {
// Function for preorder tree traversal recursively
static void countOccurrence(Node root, int K, int[] count) {
// Initialize queue for level order traversal
Queue<Node> q = new LinkedList<Node>();
q.add(root);
while (!q.isEmpty()) {
Node front_node = q.poll();
if (front_node.data == K) {
count[0]++;
}
if (front_node.left != null) {
q.add(front_node.left);
}
if (front_node.right != null) {
q.add(front_node.right);
}
}
}
// Driver code
public static void main(String[] args) {
// Binary tree as shown in example
Node root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
int K = 2;
int[] ans = {0};
// Function call
countOccurrence(root, K, ans);
System.out.println(ans[0]);
}
}
// This code is contributed by divyansh2212
# Python3 program to count frequency of k
# in given binary tree
# Structure of a tree node
class Node:
def __init__(self, data):
self.data = data
self.left = None
self.right = None
# Function for preorder tree traversal recursively
def countOccurrence(root, k):
if root is None:
return 0
count = 0
# initialize queue for level order traversal
queue = []
queue.append(root)
while(len(queue) > 0):
node = queue.pop(0)
if (node.data == k):
count += 1
if node.left is not None:
queue.append(node.left)
if node.right is not None:
queue.append(node.right)
return count
# Driver code
if __name__ == '__main__':
# Binary tree as shown in example
root = Node(1)
root.left = Node(2)
root.right = Node(2)
root.left.left = Node(4)
root.left.right = Node(2)
k = 2
# Function Call
print(countOccurrence(root, k))
// C# program to count frequency of k
// in given binary tree
using System;
using System.Collections.Generic;
// Structure of a tree node
public class Node {
public int data;
public Node left, right;
public Node(int item) {
data = item;
left = right = null;
}
}
public class BinaryTree {
Node root;
// Function for preorder tree traversal recursively
public void CountOccurrence(int k, ref int count) {
if (root == null)
return;
//initialize queue for level order traversal
Queue<Node> queue = new Queue<Node>();
queue.Enqueue(root);
while (queue.Count > 0) {
Node frontNode = queue.Dequeue();
if (frontNode.data == k)
count++;
if (frontNode.left != null)
queue.Enqueue(frontNode.left);
if (frontNode.right != null)
queue.Enqueue(frontNode.right);
}
}
// Driver code
public static void Main(string[] args) {
// Binary tree as shown in example
BinaryTree tree = new BinaryTree();
tree.root = new Node(1);
tree.root.left = new Node(2);
tree.root.right = new Node(2);
tree.root.left.left = new Node(4);
tree.root.left.right = new Node(2);
int k = 2;
int count = 0;
// Function Call
tree.CountOccurrence(k, ref count);
Console.WriteLine(count);
}
}
// Structure of a tree node
class Node {
constructor(data) {
this.data = data;
this.left = null;
this.right = null;
}
}
// Function for preorder tree traversal recursively
function countOccurrence(root, K) {
let count = 0;
// initialize queue for level order traversal
let q = [];
q.push(root);
while(q.length > 0){
let front_node = q.shift();
if(front_node.data == K) count++;
if(front_node.left) q.push(front_node.left);
if(front_node.right) q.push(front_node.right);
}
return count;
}
// Driver code
// Binary tree as shown in example
let root = new Node(1);
root.left = new Node(2);
root.right = new Node(2);
root.left.left = new Node(4);
root.left.right = new Node(2);
let K = 2;
let ans = countOccurrence(root, K);
console.log(ans);
Time Complexity: O(N) where N is the number of nodes in given Binary tree because we simply traverse the each node only once.
Auxiliary space: O(N) due to queue data structure for storing the node level-wise.
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