Burn the binary tree starting from the target node

Given a binary tree and target node. By giving the fire to the target node and fire starts to spread in a complete tree. The task is to print the sequence of the burning nodes of a binary tree.

Rules for burning the nodes :

Fire will spread constantly to the connected nodes only.
Every node takes the same time to burn.
A node burns only once.

Examples:

Input : 
                       12
                     /     \
                   13       10
                          /     \
                       14       15
                      /   \     /  \
                     21   24   22   23
target node = 14

Output :
14
21, 24, 10
15, 12
22, 23, 13

Explanation : First node 14 burns then it gives fire to it's 
neighbors(21, 24, 10) and so on. This process continues until 
the whole tree burns.


Input :
                       12
                     /     \
                  19        82
                 /        /     \
               41       15       95
                 \     /         /  \
                  2   21        7   16
target node = 41

Output :
41
2, 19
12
82
15, 95
21, 7, 16

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach :
First search the target node in a binary tree recursively. After finding the target node print it and save its left child(if exist) and right child(if exist) in a queue. and return. Now, get the size of the queue and run while loop. Print elements in the queue.

Below is the implementation of the above approach :

// C++ implementation to print the sequence  
// of burning of nodes of a binary tree 
#include <bits/stdc++.h> 
using namespace std; 
  
// A Tree node 
struct Node { 
    int key; 
    struct Node *left, *right; 
}; 
  
// Utility function to create a new node 
Node* newNode(int key) 
{ 
    Node* temp = new Node; 
    temp->key = key; 
    temp->left = temp->right = NULL; 
    return (temp); 
} 
  
// Utility function to print the sequence of burning nodes 
int burnTreeUtil(Node* root, int target, queue<Node*>& q) 
{ 
    // Base condition 
    if(root == NULL) 
    { 
        return 0; 
    } 
      
    // Condition to check whether target  
    // node is found or not in a tree 
    if(root->key == target) 
    { 
        cout<<root->key<<endl; 
        if(root->left != NULL) 
        { 
            q.push(root->left); 
        } 
        if(root->right != NULL) 
        { 
  
            q.push(root->right); 
        } 
          
        // Return statements to prevent 
        // further function calls 
        return 1; 
    } 
      
    int a = burnTreeUtil(root->left, target, q); 
          
    if(a == 1) 
    { 
        int qsize = q.size(); 
          
        // Run while loop until size of queue 
        // becomes zero 
        while(qsize--) 
        { 
            Node* temp = q.front(); 
              
            // Printing of burning nodes 
            cout<<temp->key<<" , "; 
            q.pop(); 
              
            // Check if condition for left subtree 
            if(temp->left != NULL) 
                q.push(temp->left); 
                  
            //Check if condition for right subtree 
            if(temp->right != NULL) 
                    q.push(temp->right); 
        } 
              
        if(root->right != NULL) 
            q.push(root->right); 
  
        cout<<root->key<<endl; 
              
        // Return statement it prevents further 
        // further function call 
            return 1; 
    } 
      
    int b = burnTreeUtil(root->right, target, q); 
      
    if(b == 1) 
    { 
        int qsize = q.size(); 
        // Run while loop until size of queue 
        // becomes zero 
              
        while(qsize--) 
        { 
            Node* temp = q.front(); 
                  
            //Printing of burning nodes 
            cout<<temp->key<<" , "; 
            q.pop(); 
                  
            //Check if condition for left subtree 
            if(temp->left != NULL) 
                q.push(temp->left); 
                  
            //Check if condition for left subtree 
            if(temp->right != NULL) 
                q.push(temp->right); 
        } 
          
        if(root->left != NULL) 
            q.push(root->left); 
      
        cout<<root->key<<endl; 
          
        // Return statement it prevents further 
        // further function call 
        return 1; 
  
    } 
} 
  
//Function will print the sequence of burning nodes  
void burnTree(Node* root, int target)  
{  
    queue<Node*> q;  
      
    //Function call  
    burnTreeUtil(root, target, q);  
      
    //While loop runs unless queue becomes empty  
    while(!q.empty())  
    {  
    int qSize = q.size(); 
    while(qSize > 0) 
    { 
        Node* temp = q.front();  
          
        //Printing of burning nodes  
        cout<<temp->key;  
        //Insert left child in a queue, if exist 
        if(temp->left != NULL) 
        { 
        q.push(temp->left);  
        } 
        //Insert right child in a queue, if exist 
        if(temp->right != NULL) 
        { 
        q.push(temp->right); 
        } 
          
    if(q.size()!=1)  
    cout << " , ";  
  
    q.pop();  
        qSize--; 
    } 
    cout<<endl; 
          
    }  
}  
  
// Driver Code 
int main() 
{ 
/*      10 
       /  \ 
      12  13 
          / \ 
         14 15 
        / \ / \ 
      21 22 23 24 
  
    Let us create Binary Tree as shown 
    above */
  
    Node* root = newNode(10); 
    root->left = newNode(12); 
    root->right = newNode(13); 
  
    root->right->left = newNode(14); 
    root->right->right = newNode(15); 
  
    root->right->left->left = newNode(21); 
    root->right->left->right = newNode(22); 
    root->right->right->left = newNode(23); 
    root->right->right->right = newNode(24); 
    int targetNode = 14; 
      
    // Function call 
    burnTree(root, targetNode); 
  
    return 0; 
} 

Output:

14
21 , 22 , 13
15 , 10
23 , 24 , 12

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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