Reverse zigzag Traversal of a Binary Tree
Given a Binary Tree, the task is to print the Reverse zigzag Order of the tree.
Examples:
Input:
1
/ \
2 3
/ \ \
4 5 6
Output: 6 5 4 2 3 1
Input:
5
/ \
9 3
/ \
6 4
/ \
8 7
Output: 7 8 6 4 3 9 5
Approach: The idea is to traverse the tree in a Reverse Level Order manner but with a slight modification. We will use a variable flag and initially set it’s value to one. As we complete the reverse level order traversal of the tree, from right to left we will set the value of flag to zero, so that next time we traverse the Tree from left to right and as we complete the traversal we set it’s value back to one. We will repeat this whole step until we have traversed the Binary Tree completely.
Below is the implementation of the above approach:
C++
// C++ program to print reverse // zigzag order of binary tree #include <bits/stdc++.h> using namespace std; // Binary tree node struct node { struct node* left; struct node* right; int data; }; // Function to create a new // Binary node struct node* newNode(int data) { struct node* temp = new node; temp->data = data; temp->left = NULL; temp->right = NULL; return temp; } // Recursive Function to find height // of binary tree int HeightOfTree(struct node* root) { if (root == NULL) return 0; // Compute the height of each subtree int lheight = HeightOfTree(root->left); int rheight = HeightOfTree(root->right); // Return the maximum of two return max(lheight + 1, rheight + 1); } // Function to Print nodes from right to left void Print_Level_Right_To_Left(struct node* root, int level) { if (root == NULL) return; if (level == 1) cout << root->data << " "; else if (level > 1) { Print_Level_Right_To_Left(root->right, level - 1); Print_Level_Right_To_Left(root->left, level - 1); } } // Function to Print nodes from left to right void Print_Level_Left_To_Right(struct node* root, int level) { if (root == NULL) return; if (level == 1) cout << root->data << " "; else if (level > 1) { Print_Level_Left_To_Right(root->left, level - 1); Print_Level_Left_To_Right(root->right, level - 1); } } // Function to print Reverse zigzag of // a Binary tree void PrintReverseZigZag(struct node* root) { // Flag is used to mark the change // in level int flag = 1; // Height of tree int height = HeightOfTree(root); for (int i = height; i >= 1; i--) { // If flag value is one print nodes // from right to left if (flag == 1) { Print_Level_Right_To_Left(root, i); // Mark flag as zero so that next time // tree is traversed from left to right flag = 0; } // If flag is zero print nodes // from left to right else if (flag == 0) { Print_Level_Left_To_Right(root, i); // Mark flag as one so that next time // nodes are printed from right to left flag = 1; } } } // Driver code int main() { struct node* root = newNode(5); root->left = newNode(9); root->right = newNode(3); root->left->left = newNode(6); root->right->right = newNode(4); root->left->left->left = newNode(8); root->left->left->right = newNode(7); PrintReverseZigZag(root); return 0; } |
chevron_right
filter_none
Java
// Java program to print reverse // zigzag order of binary tree class GfG { // Binary tree node static class node { node left; node right; int data; } // Function to create a new // Binary node static node newNode(int data) { node temp = new node(); temp.data = data; temp.left = null; temp.right = null; return temp; } // Recursive Function to find height // of binary tree static int HeightOfTree(node root) { if (root == null) return 0; // Compute the height of each subtree int lheight = HeightOfTree(root.left); int rheight = HeightOfTree(root.right); // Return the maximum of two return Math.max(lheight + 1, rheight + 1); } // Function to Print nodes from right to left static void Print_Level_Right_To_Left(node root, int level) { if (root == null) return; if (level == 1) System.out.print(root.data + " "); else if (level > 1) { Print_Level_Right_To_Left(root.right, level - 1); Print_Level_Right_To_Left(root.left, level - 1); } } // Function to Print nodes from left to right static void Print_Level_Left_To_Right(node root, int level) { if (root == null) return; if (level == 1) System.out.print(root.data + " "); else if (level > 1) { Print_Level_Left_To_Right(root.left, level - 1); Print_Level_Left_To_Right(root.right, level - 1); } } // Function to print Reverse zigzag of // a Binary tree static void PrintReverseZigZag(node root) { // Flag is used to mark the change // in level int flag = 1; // Height of tree int height = HeightOfTree(root); for (int i = height; i >= 1; i--) { // If flag value is one print nodes // from right to left if (flag == 1) { Print_Level_Right_To_Left(root, i); // Mark flag as zero so that next time // tree is traversed from left to right flag = 0; } // If flag is zero print nodes // from left to right else if (flag == 0) { Print_Level_Left_To_Right(root, i); // Mark flag as one so that next time // nodes are printed from right to left flag = 1; } } } // Driver code public static void main(String[] args) { node root = newNode(5); root.left = newNode(9); root.right = newNode(3); root.left.left = newNode(6); root.right.right = newNode(4); root.left.left.left = newNode(8); root.left.left.right = newNode(7); PrintReverseZigZag(root); } } // This code is contributed by Prerna Saini. |
chevron_right
filter_none
Output:
7 8 6 4 3 9 5
Recommended Posts:
- Reverse Morris traversal using Threaded Binary Tree
- ZigZag Tree Traversal
- Construct Full Binary Tree using its Preorder traversal and Preorder traversal of its mirror tree
- Given level order traversal of a Binary Tree, check if the Tree is a Min-Heap
- Density of Binary Tree in One Traversal
- Diagonal Traversal of Binary Tree
- Zig-Zag traversal of a Binary Tree using Recursion
- Boundary Traversal of binary tree
- Clockwise Spiral Traversal of Binary Tree
- If you are given two traversal sequences, can you construct the binary tree?
- Iterative diagonal traversal of binary tree
- Construct Special Binary Tree from given Inorder traversal
- Postorder traversal of Binary Tree without recursion and without stack
- Find n-th node in Postorder traversal of a Binary Tree
- Find n-th node in Preorder traversal of a Binary Tree
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.
Improved By : prerna saini