![C++ Program:
Recursive reversal of a tree.
[16] Write a method void TreeNode::reverse() (with wrapper void Tree::reverse() ) which
recursively reverses the tree.
Solution
Answer:-
1) Traverse the given tree in inorder fashion and store all odd level nodes in an auxiliary array.
For the above example given tree, contents of array become {h, i, b, j, k, l, m, c, n, o}
2) Reverse the array. The array now becomes {o, n, c, m, l, k, j, b, i, h}
3) Traverse the tree again inorder fashion. While traversing the tree, one by one take elements
from array and store elements from array to every odd level traversed node.
For the above example, we traverse ‘h’ first in above array and replace ‘h’ with ‘o’. Then we
traverse ‘i’ and replace it with n.
Program:-
// C++ program to reverse alternate levels of a binary tree
#include
#define MAX 100
using namespace std;
// A Binary Tree node
struct Node
{
char data;
struct Node *left, *right;
};
// A utility function to create a new Binary Tree Node
struct Node *newNode(char item)
{
struct Node *temp = new Node;
temp->data = item;
temp->left = temp->right = NULL;
return temp;
}
// Function to store nodes of alternate levels in an array](https://image.slidesharecdn.com/cprogramrecursivereversalofatree-230707113727-bd0070cf/85/C-ProgramRecursive-reversal-of-a-tree-16-Write-a-method-voi-pdf-1-320.jpg)
![void storeAlternate(Node *root, char arr[], int *index, int l)
{
// Base case
if (root == NULL) return;
// Store elements of left subtree
storeAlternate(root->left, arr, index, l+1);
// Store this node only if this is a odd level node
if (l%2 != 0)
{
arr[*index] = root->data;
(*index)++;
}
// Store elements of right subtree
storeAlternate(root->right, arr, index, l+1);
}
// Function to modify Binary Tree (All odd level nodes are
// updated by taking elements from array in inorder fashion)
void modifyTree(Node *root, char arr[], int *index, int l)
{
// Base case
if (root == NULL) return;
// Update nodes in left subtree
modifyTree(root->left, arr, index, l+1);
// Update this node only if this is an odd level node
if (l%2 != 0)
{
root->data = arr[*index];
(*index)++;
}
// Update nodes in right subtree
modifyTree(root->right, arr, index, l+1);
}
// A utility function to reverse an array from index
// 0 to n-1
void reverse(char arr[], int n)
{](https://image.slidesharecdn.com/cprogramrecursivereversalofatree-230707113727-bd0070cf/85/C-ProgramRecursive-reversal-of-a-tree-16-Write-a-method-voi-pdf-2-320.jpg)
![int l = 0, r = n-1;
while (l < r)
{
int temp = arr[l];
arr[l] = arr[r];
arr[r] = temp;
l++; r--;
}
}
// The main function to reverse alternate nodes of a binary tree
void reverseAlternate(struct Node *root)
{
// Create an auxiliary array to store nodes of alternate levels
char *arr = new char[MAX];
int index = 0;
// First store nodes of alternate levels
storeAlternate(root, arr, &index, 0);
// Reverse the array
reverse(arr, index);
// Update tree by taking elements from array
index = 0;
modifyTree(root, arr, &index, 0);
}
// A utility function to print indorder traversal of a
// binary tree
void printInorder(struct Node *root)
{
if (root == NULL) return;
printInorder(root->left);
cout << root->data << " ";
printInorder(root->right);
}
// Driver Program to test above functions
int main()
{
struct Node *root = newNode('a');](https://image.slidesharecdn.com/cprogramrecursivereversalofatree-230707113727-bd0070cf/85/C-ProgramRecursive-reversal-of-a-tree-16-Write-a-method-voi-pdf-3-320.jpg)
C++ ProgramRecursive reversal of a tree.[16] Write a method voi.pdf
- 1. C++ Program: Recursive reversal of a tree. [16] Write a method void TreeNode::reverse() (with wrapper void Tree::reverse() ) which recursively reverses the tree. Solution Answer:- 1) Traverse the given tree in inorder fashion and store all odd level nodes in an auxiliary array. For the above example given tree, contents of array become {h, i, b, j, k, l, m, c, n, o} 2) Reverse the array. The array now becomes {o, n, c, m, l, k, j, b, i, h} 3) Traverse the tree again inorder fashion. While traversing the tree, one by one take elements from array and store elements from array to every odd level traversed node. For the above example, we traverse ‘h’ first in above array and replace ‘h’ with ‘o’. Then we traverse ‘i’ and replace it with n. Program:- // C++ program to reverse alternate levels of a binary tree #include #define MAX 100 using namespace std; // A Binary Tree node struct Node { char data; struct Node *left, *right; }; // A utility function to create a new Binary Tree Node struct Node *newNode(char item) { struct Node *temp = new Node; temp->data = item; temp->left = temp->right = NULL; return temp; } // Function to store nodes of alternate levels in an array
- 2. void storeAlternate(Node *root, char arr[], int *index, int l) { // Base case if (root == NULL) return; // Store elements of left subtree storeAlternate(root->left, arr, index, l+1); // Store this node only if this is a odd level node if (l%2 != 0) { arr[*index] = root->data; (*index)++; } // Store elements of right subtree storeAlternate(root->right, arr, index, l+1); } // Function to modify Binary Tree (All odd level nodes are // updated by taking elements from array in inorder fashion) void modifyTree(Node *root, char arr[], int *index, int l) { // Base case if (root == NULL) return; // Update nodes in left subtree modifyTree(root->left, arr, index, l+1); // Update this node only if this is an odd level node if (l%2 != 0) { root->data = arr[*index]; (*index)++; } // Update nodes in right subtree modifyTree(root->right, arr, index, l+1); } // A utility function to reverse an array from index // 0 to n-1 void reverse(char arr[], int n) {
- 3. int l = 0, r = n-1; while (l < r) { int temp = arr[l]; arr[l] = arr[r]; arr[r] = temp; l++; r--; } } // The main function to reverse alternate nodes of a binary tree void reverseAlternate(struct Node *root) { // Create an auxiliary array to store nodes of alternate levels char *arr = new char[MAX]; int index = 0; // First store nodes of alternate levels storeAlternate(root, arr, &index, 0); // Reverse the array reverse(arr, index); // Update tree by taking elements from array index = 0; modifyTree(root, arr, &index, 0); } // A utility function to print indorder traversal of a // binary tree void printInorder(struct Node *root) { if (root == NULL) return; printInorder(root->left); cout << root->data << " "; printInorder(root->right); } // Driver Program to test above functions int main() { struct Node *root = newNode('a');
- 4. root->left = newNode('b'); root->right = newNode('c'); root->left->left = newNode('d'); root->left->right = newNode('e'); root->right->left = newNode('f'); root->right->right = newNode('g'); root->left->left->left = newNode('h'); root->left->left->right = newNode('i'); root->left->right->left = newNode('j'); root->left->right->right = newNode('k'); root->right->left->left = newNode('l'); root->right->left->right = newNode('m'); root->right->right->left = newNode('n'); root->right->right->right = newNode('o'); cout << "Inorder Traversal of given tree "; printInorder(root); reverseAlternate(root); cout << " Inorder Traversal of modified tree "; printInorder(root); return 0; }