Reverse tree path using Queue

Given a tree and a node, the task is to reverse the path till the given Node and print the in-order traversal of the modified tree.
Examples: 
 

Input:  
             7
           /   \
          6     5
         / \   / \
        4   3 2   1    
Node = 4 
Output: 7 6 3 4 2 5 1
The path from root to node 4 is 7 -> 6 -> 4
Reversing this path, the modified tree will be:
             4
           /   \
          6     5
         / \   / \
        7   3 2   1 
whose in-order traversal is 7 6 3 4 2 5 1

Input:
            7
         /    \
        6       5
       / \     / \
      4  3     2  1   
Node = 2 
Output: 4 6 3 2 7 5 1

Approach:

  • First store all the nodes on the given path in a queue.
  • If the key is found then replace this node data with the front of queue data and pop the front.
  • Keep on performing this operation in a recursive way up to the root and the path will be reversed in the original tree.
  • Now, print the in-order traversal of the modified tree.

Below is the implementation of the above approach: 
 

C++

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// A Binary Tree Node
struct Node {
    int data;
    struct Node *left, *right;
};
 
// Function to reverse the tree path
queue<int> reverseTreePathUtil(Node* root, int data,
                               queue<int> q1)
{
    queue<int> emptyQueue;
 
    // If root is null then return
    // an empty queue
    if (root == NULL)
        return emptyQueue;
 
    // If the node is found
    if (root->data == data) {
 
        // Replace it with the queue's front
        q1.push(root->data);
        root->data = q1.front();
        q1.pop();
        return q1;
    }
 
    // Push data into the queue for
    // storing data from start to end
    q1.push(root->data);
 
    // If the returned queue is empty then
    // it means that the left sub-tree doesn't
    // contain the required node
    queue<int> left = reverseTreePathUtil(root->left,
                                          data, q1);
 
    // If the returned queue is empty then
    // it means that the right sub-tree doesn't
    // contain the required node
    queue<int> right = reverseTreePathUtil(root->right,
                                           data, q1);
 
    // If the required node is found
    // in the right sub-tree
    if (!right.empty()) {
 
        // Replace with the queue's front
        root->data = right.front();
        right.pop();
        return right;
    }
 
    // If the required node is found
    // in the right sub-tree
    if (!left.empty()) {
 
        // Replace with the queue's front
        root->data = left.front();
        left.pop();
        return left;
    }
 
    // Return emptyQueue if path
    // is not found
    return emptyQueue;
}
 
// Function to call reverseTreePathUtil
// to reverse the tree path
void reverseTreePath(Node* root, int data)
{
    queue<int> q1;
    // reverse tree path
    reverseTreePathUtil(root, data, q1);
}
 
// Function to print the in-order
// traversal of the tree
void inorder(Node* root)
{
    if (root != NULL) {
        inorder(root->left);
        cout << root->data << " ";
        inorder(root->right);
    }
}
 
// Utility function to create a new tree node
Node* newNode(int data)
{
    Node* temp = new Node;
    temp->data = data;
    temp->left = temp->right = NULL;
    return temp;
}
 
// Driver code
int main()
{
    Node* root = newNode(7);
    root->left = newNode(6);
    root->right = newNode(5);
    root->left->left = newNode(4);
    root->left->right = newNode(3);
    root->right->left = newNode(2);
    root->right->right = newNode(1);
 
    int data = 4;
 
    // Function call to reverse the path
    reverseTreePath(root, data);
 
    // Print the in-order traversal
    // of the modified tree
    inorder(root);
 
    return 0;
}

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Python3














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# Python3 implementation of the 


# above approach


  


# A Binary Tree Node


class Node:


     


    def __init__(self, data):


       


        self.data = data


        self.left = None


        self.right = None


  


# Function to reverse the 


# tree path


def reverseTreePathUtil(root,


                        data, q1):


 


    emptyQueue = []


  


    # If root is null then 


    # return an empty queue


    if (root == None):


        return emptyQueue;


  


    # If the node is found


    if (root.data == data):


  


        # Replace it with the 


        # queue's front


        q1.append(root.data);


        root.data = q1[0]


        q1.pop(0);


        return q1;    


  


    # Push data into the 


    # queue for storing 


    # data from start to end


    q1.append(root.data);


  


    # If the returned queue 


    # is empty then it means


    # that the left sub-tree 


    # doesn't contain the 


    # required node


    left = reverseTreePathUtil(root.left,


                               data, q1);


  


    # If the returned queue is empty 


    # then it means that the right 


    # sub-tree doesn't contain the 


    # required node


    right = reverseTreePathUtil(root.right,


                                data, q1);


  


    # If the required node is found


    # in the right sub-tree


    if len(right) != 0:


  


        # Replace with the queue's 


        # front


        root.data = right[0]


        right.pop(0);


        return right;


  


    # If the required node 


    # is found in the right 


    # sub-tree


    if len(left) != 0:


  


        # Replace with the 


        # queue's front


        root.data = left[0]


        left.pop(0);


        return left;


  


    # Return emptyQueue 


    # if path is not found


    return emptyQueue;


  


# Function to call reverseTreePathUtil


# to reverse the tree path


def reverseTreePath(root, data):


 


    q1 = []


     


    # reverse tree path


    reverseTreePathUtil(root, 


                        data, q1);


  


# Function to print the in-order


# traversal of the tree


def inorder(root):


 


    if (root != None):


        inorder(root.left);


        print(root.data, 


              end = ' ')


        inorder(root.right); 


  


# Utility function to create 


# a new tree node


def newNode(data):


 


    temp = Node(data)


    return temp;


 


# Driver code 


if __name__ == "__main__":


     


    root = newNode(7);


    root.left = newNode(6);


    root.right = newNode(5);


    root.left.left = newNode(4);


    root.left.right = newNode(3);


    root.right.left = newNode(2);


    root.right.right = newNode(1);


  


    data = 4;


  


    # Function call to reverse 


    # the path


    reverseTreePath(root, data);


  


    # Print the in-order traversal


    # of the modified tree


    inorder(root);


  


# This code is contributed by Rutvik_56



















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Output: 


7 6 3 4 2 5 1




 




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