# 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++

 `// C++ implementation of the approach` `#include ` `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;` `}`

## Python3

 `# 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`

Output:

```7 6 3 4 2 5 1

```

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