Given a Binary Tree, the task is to print the zigzag order of the tree.
Examples:
Input : 7 / \ 6 5 / / 4 3 / \ 2 1 Output : 7 5 6 4 3 1 2 Input : 1 / \ 2 3 / \ 4 5 Output : 1 3 2 4 5
We have already discussed the zigzag traversal using an iterative approach, in this post we will solve it using Recursion.
Recursive Approach: The idea is to traverse the tree in a Level Order manner but in a slightly different manner. We will use a variable flag and initially set it’s value to zero. As we complete the level order traversal of the tree, from right to left we will set the value of flag to one, so that next time we can traverse the Tree from left to right and as we complete the traversal we will set it’s value back to zero. 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 zigzag // traversal of a binary tree // using Recursion #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 Tree 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; int lheight = heightOfTree(root->left); int rheight = heightOfTree(root->right); return max(lheight + 1 ,rheight + 1); } // Function to print nodes from right to left void printRightToLeft( struct node* root , int level) { if (root == NULL) return ; if (level == 1) cout << root->data << " " ; else if (level > 1) { printRightToLeft(root->right ,level - 1); printRightToLeft(root->left ,level - 1); } } // Function to print nodes from left to right void printLeftToRight( struct node* root , int level) { if (root == NULL) return ; if (level == 1) cout << root->data << " " ; else if (level > 1) { printLeftToRight(root->left ,level - 1); printLeftToRight(root->right ,level - 1); } } // Function to print Reverse ZigZag of // a Binary tree void printZigZag( struct node* root ) { // Flag is used to mark the change // in level int flag = 0; // Height of tree int height = heightOfTree(root); for ( int i = 1 ; i <= height ; i++) { // If flag value is one print nodes // from right to left if (flag == 1) { printRightToLeft(root ,i); // Mark flag as zero so that next time // nodes are printed from left to right flag = 0; } // If flag is zero print nodes // from left to right else if (flag == 0) { printLeftToRight(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(7); root->left = newNode(4); root->right = newNode(5); root->left->left = newNode(9); root->right->right = newNode(10); root->left->left->left = newNode(6); root->left->left->right = newNode(11); printZigZag(root); return 0; } |
Java
// Java program to print zigzag // traversal of a binary tree // using Recursion import java.util.*; // Binary tree node class Node { Node left; Node right; int data; Node( int data) { this .data = data; left = null ; right = null ; } } class Main { // Function to create a new // Binary Tree Node static Node newNode( int data) { Node temp = new Node(data); 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 ; int lheight = heightOfTree(root.left); int rheight = heightOfTree(root.right); return Math.max(lheight + 1 , rheight + 1 ); } // Function to print nodes from right to left static void printRightToLeft(Node root, int level) { if (root == null ) return ; if (level == 1 ) System.out.print(root.data + " " ); else if (level > 1 ) { printRightToLeft(root.right, level - 1 ); printRightToLeft(root.left, level - 1 ); } } // Function to print nodes from left to right static void printLeftToRight(Node root, int level) { if (root == null ) return ; if (level == 1 ) System.out.print(root.data + " " ); else if (level > 1 ) { printLeftToRight(root.left, level - 1 ); printLeftToRight(root.right, level - 1 ); } } // Function to print Reverse ZigZag of // a Binary tree static void printZigZag(Node root) { // Flag is used to mark the change // in level int flag = 0 ; // Height of tree int height = heightOfTree(root); for ( int i = 1 ; i <= height; i++) { // If flag value is one print nodes // from right to left if (flag == 1 ) { printRightToLeft(root, i); // Mark flag as zero so that next time // nodes are printed from left to right flag = 0 ; } // If flag is zero print nodes // from left to right else if (flag == 0 ) { printLeftToRight(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( 7 ); root.left = newNode( 4 ); root.right = newNode( 5 ); root.left.left = newNode( 9 ); root.right.right = newNode( 10 ); root.left.left.left = newNode( 6 ); root.left.left.right = newNode( 11 ); printZigZag(root); } } |
Python3
# Python3 program to print zigzag traversal # of a binary tree using Recursion # Binary tree node class Node: def __init__( self , data): self .data = data self .left = None self .right = None # Recursive Function to find height # of binary tree def heightOfTree(root): if root = = None : return 0 lheight = heightOfTree(root.left) rheight = heightOfTree(root.right) return max (lheight + 1 , rheight + 1 ) # Function to print nodes from right to left def printRightToLeft(root, level): if root = = None : return if level = = 1 : print (root.data, end = " " ) elif level > 1 : printRightToLeft(root.right, level - 1 ) printRightToLeft(root.left, level - 1 ) # Function to print nodes from left to right def printLeftToRight(root, level): if root = = None : return if level = = 1 : print (root.data, end = " " ) elif level > 1 : printLeftToRight(root.left, level - 1 ) printLeftToRight(root.right, level - 1 ) # Function to print Reverse ZigZag of # a Binary tree def printZigZag(root): # Flag is used to mark the # change in level flag = 0 # Height of tree height = heightOfTree(root) for i in range ( 1 , height + 1 ): # If flag value is one print nodes # from right to left if flag = = 1 : printRightToLeft(root, i) # Mark flag as zero so that next time # nodes are printed from left to right flag = 0 # If flag is zero print nodes # from left to right elif flag = = 0 : printLeftToRight(root, i) # Mark flag as one so that next time # nodes are printed from right to left flag = 1 # Driver code if __name__ = = "__main__" : root = Node( 7 ) root.left = Node( 4 ) root.right = Node( 5 ) root.left.left = Node( 9 ) root.right.right = Node( 10 ) root.left.left.left = Node( 6 ) root.left.left.right = Node( 11 ) printZigZag(root) # This code is contributed by Rituraj Jain |
C#
// C# program to print zigzag // traversal of a binary tree // using Recursion using System; class GfG { // Binary tree node public class node { public node left; public node right; public int data; } // Function to create a new // Binary Tree 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; int lheight = heightOfTree(root.left); int rheight = heightOfTree(root.right); return Math.Max(lheight + 1 ,rheight + 1); } // Function to print nodes from right to left static void printRightToLeft(node root , int level) { if (root == null ) return ; if (level == 1) Console.Write(root.data + " " ) ; else if (level > 1) { printRightToLeft(root.right ,level - 1); printRightToLeft(root.left ,level - 1); } } // Function to print nodes from left to right static void printLeftToRight(node root , int level) { if (root == null ) return ; if (level == 1) Console.Write(root.data + " " ) ; else if (level > 1) { printLeftToRight(root.left ,level - 1); printLeftToRight(root.right ,level - 1); } } // Function to print Reverse ZigZag of // a Binary tree static void printZigZag(node root ) { // Flag is used to mark the change // in level int flag = 0; // Height of tree int height = heightOfTree(root); for ( int i = 1 ; i <= height ; i++) { // If flag value is one print nodes // from right to left if (flag == 1) { printRightToLeft(root, i); // Mark flag as zero so that next time // nodes are printed from left to right flag = 0; } // If flag is zero print nodes // from left to right else if (flag == 0) { printLeftToRight(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() { node root = newNode(7); root.left = newNode(4); root.right = newNode(5); root.left.left = newNode(9); root.right.right = newNode(10); root.left.left.left = newNode(6); root.left.left.right = newNode(11); printZigZag(root); } } /* This code contributed by PrinciRaj1992 */ |
Javascript
<script> // JavaScript program to print zigzag // traversal of a binary tree // using Recursion // Binary tree node class node { constructor(data) { this .left = null ; this .right = null ; this .data = data; } } // Function to create a new // Binary Tree Node function newNode(data) { let temp = new node(data); return temp; } // Recursive Function to find height // of binary tree function heightOfTree(root) { if (root == null ) return 0; let lheight = heightOfTree(root.left); let rheight = heightOfTree(root.right); return Math.max(lheight + 1 ,rheight + 1); } // Function to print nodes from right to left function printRightToLeft(root, level) { if (root == null ) return ; if (level == 1) document.write(root.data + " " ) ; else if (level > 1) { printRightToLeft(root.right ,level - 1); printRightToLeft(root.left ,level - 1); } } // Function to print nodes from left to right function printLeftToRight(root, level) { if (root == null ) return ; if (level == 1) document.write(root.data + " " ) ; else if (level > 1) { printLeftToRight(root.left ,level - 1); printLeftToRight(root.right ,level - 1); } } // Function to print Reverse ZigZag of // a Binary tree function printZigZag(root) { // Flag is used to mark the change // in level let flag = 0; // Height of tree let height = heightOfTree(root); for (let i = 1 ; i <= height ; i++) { // If flag value is one print nodes // from right to left if (flag == 1) { printRightToLeft(root ,i); // Mark flag as zero so that next time // nodes are printed from left to right flag = 0; } // If flag is zero print nodes // from left to right else if (flag == 0) { printLeftToRight(root ,i); // Mark flag as one so that next time // nodes are printed from right to left flag = 1; } } } let root = newNode(7); root.left = newNode(4); root.right = newNode(5); root.left.left = newNode(9); root.right.right = newNode(10); root.left.left.left = newNode(6); root.left.left.right = newNode(11); printZigZag(root); </script> |
7 5 4 9 10 11 6
Time Complexity: O(N)
Auxiliary Space: O(N)
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