Iterative Method To Print Left View of a Binary Tree
Given a Binary Tree, print it’s left view. Left view of a Binary Tree is a set of nodes visible when tree is seen from the left side .
Examples:
Input : 1
/ \
2 3
/ \ / \
4 5 6 7
Output : 1 2 4
Input : 1
/ \
2 3
\ /
4 5
\
6
/ \
7 8
Output : 1 2 4 6 7
We have already discussed this problem using the Recursion method, here iterative approach is used to solve the above problem.
The idea is to do level order traversal of the Tree using a queue and print the first node at each level.
While doing level order traversal, after traversing all node at each level, push a NULL delimiter to mark the end of the current level. So, do the level order traversal of the tree. Print the first node at each level in the tree and push the children of all nodes at each level in the queue until a NULL delimiter is encountered.
Below is the implementation of above approach:
C++
// C++ program to print the// left view of Binary Tree#include <bits/stdc++.h>using namespace std;// A Binary Tree Nodestruct node { int data; struct node *left, *right;};// A utility function to create a new// Binary Tree nodestruct node* newNode(int item){ struct node* temp = new node; temp->data = item; temp->left = NULL; temp->right = NULL; return temp;}// Utility function to print the left view of// the binary treevoid leftViewUtil(struct node* root, queue<node*>& q){ if (root == NULL) return; // Push root q.push(root); // Delimiter q.push(NULL); while (!q.empty()) { node* temp = q.front(); if (temp) { // Prints first node // of each level cout << temp->data << " "; // Push children of all nodes at // current level while (q.front() != NULL) { // If left child is present // push into queue if (temp->left) q.push(temp->left); // If right child is present // push into queue if (temp->right) q.push(temp->right); // Pop the current node q.pop(); temp = q.front(); } // Push delimiter // for the next level q.push(NULL); } // Pop the delimiter of // the previous level q.pop(); }}// Function to print the leftView// of Binary Treevoid leftView(struct node* root){ // Queue to store all // the nodes of the tree queue<node*> q; leftViewUtil(root, q);}// Driver Codeint main(){ struct node* root = newNode(10); root->left = newNode(12); root->right = newNode(3); root->left->right = newNode(4); root->right->left = newNode(5); root->right->left->right = newNode(6); root->right->left->right->left = newNode(18); root->right->left->right->right = newNode(7); leftView(root); return 0;} |
Java
// Java program to print the// left view of Binary Treeimport java.util.*;class GFG{// A Binary Tree Nodestatic class node{ int data; node left, right;};// A utility function to create a new// Binary Tree nodestatic node newNode(int item){ node temp = new node(); temp.data = item; temp.left = null; temp.right = null; return temp;}static Queue<node> q;// Utility function to print the left view of// the binary treestatic void leftViewUtil( node root ){ if (root == null) return; // add root q.add(root); // Delimiter q.add(null); while (q.size() > 0) { node temp = q.peek(); if (temp != null) { // Prints first node // of each level System.out.print(temp.data + " "); // add children of all nodes at // current level while (q.peek() != null) { // If left child is present // add into queue if (temp.left != null) q.add(temp.left); // If right child is present // add into queue if (temp.right != null) q.add(temp.right); // remove the current node q.remove(); temp = q.peek(); } // add delimiter // for the next level q.add(null); } // remove the delimiter of // the previous level q.remove(); }}// Function to print the leftView// of Binary Treestatic void leftView( node root){ // Queue to store all // the nodes of the tree q = new LinkedList<node>(); leftViewUtil(root);}// Driver Codepublic static void main(String args[]){ node root = newNode(10); root.left = newNode(12); root.right = newNode(3); root.left.right = newNode(4); root.right.left = newNode(5); root.right.left.right = newNode(6); root.right.left.right.left = newNode(18); root.right.left.right.right = newNode(7); leftView(root);}}// This code is contributed by Arnab Kundu |
Python3
# Python3 program to print the# left view of Binary Tree# Binary Tree Node""" utility that allocates a newNodewith the given key """class newNode: # Construct to create a newNode def __init__(self, key): self.data = key self.left = None self.right = None self.hd=0# Utility function to print the left# view of the binary treedef leftViewUtil(root, q) : if (root == None) : return # append root q.append(root) # Delimiter q.append(None) while (len(q)): temp = q[0] if (temp): # Prints first node of each level print(temp.data, end = " ") # append children of all nodes # at current level while (q[0] != None) : temp = q[0] # If left child is present # append into queue if (temp.left) : q.append(temp.left) # If right child is present # append into queue if (temp.right) : q.append(temp.right) # Pop the current node q.pop(0) # append delimiter # for the next level q.append(None) # Pop the delimiter of # the previous level q.pop(0) # Function to print the leftView# of Binary Treedef leftView(root): # Queue to store all # the nodes of the tree q = [] leftViewUtil(root, q)# Driver Codeif __name__ == '__main__': root = newNode(10) root.left = newNode(12) root.right = newNode(3) root.left.right = newNode(4) root.right.left = newNode(5) root.right.left.right = newNode(6) root.right.left.right.left = newNode(18) root.right.left.right.right = newNode(7) leftView(root)# This code is contributed by# Shubham Singh(SHUBHAMSINGH10) |
C#
// C# program to print the// left view of Binary Treeusing System;using System.Collections.Generic; class GFG{// A Binary Tree Nodepublic class node{ public int data; public node left, right;};// A utility function to create a new// Binary Tree nodestatic node newNode(int item){ node temp = new node(); temp.data = item; temp.left = null; temp.right = null; return temp;}static Queue<node> q = new Queue<node>();// Utility function to print the left view of// the binary treestatic void leftViewUtil( node root ){ if (root == null) return; // add root q.Enqueue(root); // Delimiter q.Enqueue(null); while (q.Count > 0) { node temp = q.Peek(); if (temp != null) { // Prints first node // of each level Console.Write(temp.data + " "); // add children of all nodes at // current level while (q.Peek() != null) { // If left child is present // add into queue if (temp.left != null) q.Enqueue(temp.left); // If right child is present // add into queue if (temp.right != null) q.Enqueue(temp.right); // remove the current node q.Dequeue(); temp = q.Peek(); } // add delimiter // for the next level q.Enqueue(null); } // remove the delimiter of // the previous level q.Dequeue(); }}// Function to print the leftView// of Binary Treestatic void leftView( node root){ // Queue to store all // the nodes of the tree q = new Queue<node>(); leftViewUtil(root);}// Driver Codepublic static void Main(String []args){ node root = newNode(10); root.left = newNode(12); root.right = newNode(3); root.left.right = newNode(4); root.right.left = newNode(5); root.right.left.right = newNode(6); root.right.left.right.left = newNode(18); root.right.left.right.right = newNode(7); leftView(root);}}// This code is contributed by 29AjayKumar |
Javascript
<script> // JavaScript program to print the left view of Binary Tree // Binary Tree Node class node { constructor(item) { this.left = null; this.right = null; this.data = item; } } // A utility function to create a new // Binary Tree node function newNode(item) { let temp = new node(item); return temp; } let q = []; // Utility function to print the left view of // the binary tree function leftViewUtil(root) { if (root == null) return; // add root q.push(root); // Delimiter q.push(null); while (q.length > 0) { let temp = q[0]; if (temp != null) { // Prints first node // of each level document.write(temp.data + " "); // add children of all nodes at // current level while (q[0] != null) { // If left child is present // add into queue if (temp.left != null) q.push(temp.left); // If right child is present // add into queue if (temp.right != null) q.push(temp.right); // remove the current node q.shift(); temp = q[0]; } // add delimiter // for the next level q.push(null); } // remove the delimiter of // the previous level q.shift(); } } // Function to print the leftView // of Binary Tree function leftView(root) { // Queue to store all // the nodes of the tree q = []; leftViewUtil(root); } let root = newNode(10); root.left = newNode(12); root.right = newNode(3); root.left.right = newNode(4); root.right.left = newNode(5); root.right.left.right = newNode(6); root.right.left.right.left = newNode(18); root.right.left.right.right = newNode(7); leftView(root);</script> |
Output:
10 12 4 6 18
Time Complexity: O(N) where N is the number of vertices in the binary tree.
Auxiliary Space: O(N).
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