Given a Binary Tree, where each node contains an extra empty pointer initially null. The task is to connect all nodes of the binary tree to their left neighbor at the same level using this extra pointer.
Examples:
Input : A / \ B C / \ \ D E F Output : NULL<--A / \ NULL<--B<--C / \ \ NULL<--D<--E<--F
Approach:
We can use the Pre-order traversal of the tree passing the level of the node at each call. The root node is at level 0. While traversing we store the recently seen node at that level in an array of node pointers. The pre-order traversal ensures that the node in the array at a particular level is left neighbor of the upcoming node at the same level.
Below is the implementation of the above approach:
// CPP program to connect nodes // at same level using extended // pre-order traversal #include <bits/stdc++.h> #include <iostream> using namespace std;
// Binary tree node, with extra pointer leftNeighbour // to store the neighbour to left nodes class node {
public :
int data;
node* left;
node* right;
node* leftNeighbour;
/* Constructor that allocates a new node with the
given data and NULL left and right pointers. */
node( int data)
{
this ->data = data;
this ->left = NULL;
this ->right = NULL;
this ->leftNeighbour = NULL;
}
}; // Array to store the recent visited // node at particular level represented // by indices node* a[100]; // Function to connect nodes using preorder // traversal void connectNodes(node* p, int l)
{ if (p == NULL)
return ;
// assigning left neighbor
p->leftNeighbour = a[l];
// updating value of the recent
// node at level
a[l] = p;
connectNodes(p->left, l + 1);
connectNodes(p->right, l + 1);
} // Utility function to connect nodes to neighbours // using preorder traversal void connectNodesUtil(node* root)
{ // Initialize nodes at every level to NULL
for ( int i = 0; i < 100; i++)
a[i] = NULL;
// Populates next left pointer in all nodes
connectNodes(root, 0);
// Let us check the values of next left pointers
cout << "Following are populated leftNeighbour"
<< " pointers in the tree:\n" ;
cout << "leftNeighbour of " << root->data << " is "
<< (root->leftNeighbour ?
root->leftNeighbour->data : -1) << endl;
cout << "leftNeighbour of " << root->left->data << " is "
<< (root->left->leftNeighbour ?
root->left->leftNeighbour->data : -1) << endl;
cout << "leftNeighbour of " << root->right->data << " is "
<< (root->right->leftNeighbour ?
root->right->leftNeighbour->data : -1) << endl;
cout << "leftNeighbour of " << root->left->left->data << " is "
<< (root->left->left->leftNeighbour ?
root->left->left->leftNeighbour->data : -1) << endl;
} // Driver Code int main()
{ /* Constructed binary tree is
10
/ \
8 2
/
3
*/
node* root = new node(10);
root->left = new node(8);
root->right = new node(2);
root->left->left = new node(3);
connectNodesUtil(root);
return 0;
} |
// Java program to connect nodes // at same level using extended // pre-order traversal import java.util.*;
class GFG
{ // Binary tree node, with extra pointer leftNeighbour // to store the neighbour to left nodes static class node
{ int data;
node left;
node right;
node leftNeighbour;
/* Constructor that allocates a new node with the
given data and null left and right pointers. */
node( int data)
{
this .data = data;
this .left = null ;
this .right = null ;
this .leftNeighbour = null ;
}
} // Array to store the recent visited // node at particular level represented // by indices static node a[] = new node[ 100 ];
// Function to connect nodes using preorder // traversal static void connectNodes(node p, int l)
{ if (p == null )
return ;
// assigning left neighbor
p.leftNeighbour = a[l];
// updating value of the recent
// node at level
a[l] = p;
connectNodes(p.left, l + 1 );
connectNodes(p.right, l + 1 );
} // Utility function to connect nodes to neighbours // using preorder traversal static void connectNodesUtil(node root)
{ // Initialize nodes at every level to null
for ( int i = 0 ; i < 100 ; i++)
a[i] = new node(- 1 );
// Populates next left pointer in all nodes
connectNodes(root, 0 );
// Let us check the values of next left pointers
System.out.println( "Following are populated leftNeighbour" +
" pointers in the tree:" );
System.out.println( "leftNeighbour of " + root.data +
" is " + (root.leftNeighbour != null ?
root.leftNeighbour.data : - 1 ));
System.out.println( "leftNeighbour of " + root.left.data +
" is " + (root.left.leftNeighbour != null ?
root.left.leftNeighbour.data : - 1 ));
System.out.println( "leftNeighbour of " + root.right.data +
" is " + (root.right.leftNeighbour != null ?
root.right.leftNeighbour.data : - 1 ) );
System.out.println( "leftNeighbour of " + root.left.left.data +
" is " + (root.left.left.leftNeighbour != null ?
root.left.left.leftNeighbour.data : - 1 ));
} // Driver Code public static void main(String args[])
{ /* Constructed binary tree is
10
/ \
8 2
/
3
*/
node root = new node( 10 );
root.left = new node( 8 );
root.right = new node( 2 );
root.left.left = new node( 3 );
connectNodesUtil(root);
} } // This code is contributed by Arnab Kundu |
# Python3 program to connect nodes # at same level using extended # pre-order traversal # Binary tree node, with extra # pointer leftNeighbour to store # the neighbour to left nodes class node:
def __init__( self , x):
self .data = x
self .left = None
self .right = None
self .leftNeighbour = None
# Array to store the recent visited # node at particular level represented # by indices a = [ None for i in range ( 100 )]
# Function to connect nodes using # preorder traversal def connectNodes(p, l):
if (p = = None ):
return
# assigning left neighbor
p.leftNeighbour = a[l]
# updating value of the
# recent node at level
a[l] = p
connectNodes(p.left,
l + 1 )
connectNodes(p.right,
l + 1 )
# Utility function to connect # nodes to neighbours # using preorder traversal def connectNodesUtil(root):
# Populates next left
# pointer in all nodes
connectNodes(root, 0 )
# Let us check the values
# of next left pointers
print ( "Following are populated" +
"leftNeighbour pointers in" +
"the tree:" )
x = - 1
if root.leftNeighbour:
x = root.leftNeighbour.data
print ( "leftNeighbour of " ,
root.data, " is " , x)
x = - 1
if root.left.leftNeighbour:
x = root.left.leftNeighbour.data
print ( "leftNeighbour of " ,
root.left.data, " is " , x)
x = - 1
if root.right.leftNeighbour:
x = root.right.leftNeighbour.data
print ( "leftNeighbour of " ,
root.right.data, " is " , x)
x = - 1
if root.left.left.leftNeighbour:
x = root.left.left.leftNeighbour.data
print ( "leftNeighbour of " ,
root.left.left.data, " is " , x)
# Driver Code if __name__ = = '__main__' :
# /* Constructed binary tree is
# 10
# / \
# 8 2
# /
# 3
# */
root = node( 10 )
root.left = node( 8 )
root.right = node( 2 )
root.left.left = node( 3 )
connectNodesUtil(root)
# This code is contributed by Mohit Kumar 29 |
// C# program to connect nodes // at same level using extended // pre-order traversal using System;
// Binary tree node, with extra pointer leftNeighbour // to store the neighbour to left nodes class node
{ public int data;
public node left;
public node right;
public node leftNeighbour;
/* Constructor that allocates a new node with the
given data and null left and right pointers. */
public node( int data)
{
this .data = data;
this .left = null ;
this .right = null ;
this .leftNeighbour = null ;
}
} class GFG
{ static node root;
// Array to store the recent visited
// node at particular level represented
// by indices
static node[] a = new node[100];
// Function to connect nodes using preorder
// traversal
static void connectNodes(node p, int l)
{
if (p == null )
{
return ;
}
// assigning left neighbor
p.leftNeighbour = a[l];
// updating value of the recent
// node at level
a[l] = p;
connectNodes(p.left, l + 1);
connectNodes(p.right, l + 1);
}
// Utility function to connect nodes to neighbours
// using preorder traversal
static void connectNodesUtil(node root)
{
// Initialize nodes at every level to null
for ( int i = 0; i < 100; i++)
{
a[i] = new node(-1);
}
// Populates next left pointer in all nodes
connectNodes(root, 0);
// Let us check the values of next left pointers
Console.WriteLine( "Following are populated leftNeighbour" +
" pointers in the tree:" );
Console.WriteLine( "leftNeighbour of " + root.data +
" is " + (root.leftNeighbour != null ?
root.leftNeighbour.data : -1));
Console.WriteLine( "leftNeighbour of " + root.left.data +
" is " + (root.left.leftNeighbour != null ?
root.left.leftNeighbour.data : -1));
Console.WriteLine( "leftNeighbour of " + root.right.data +
" is " + (root.right.leftNeighbour != null ?
root.right.leftNeighbour.data : -1) );
Console.WriteLine( "leftNeighbour of " + root.left.left.data +
" is " + (root.left.left.leftNeighbour != null ?
root.left.left.leftNeighbour.data : -1));
}
// Driver Code
static public void Main ()
{
/* Constructed binary tree is
10
/ \
8 2
/
3
*/
GFG.root = new node(10);
GFG.root.left = new node(8);
GFG.root.right = new node(2);
GFG.root.left.left = new node(3);
connectNodesUtil(root);
}
} // This code is contributed by avanitrachhadiya2155 |
<script> // Javascript program to connect nodes // at same level using extended // pre-order traversal // Binary tree node, with extra pointer leftNeighbour // to store the neighbour to left nodes class node { /* Constructor that allocates a new node with the
given data and null left and right pointers. */
constructor(data)
{
this .data = data;
this .left = null ;
this .right = null ;
this .leftNeighbour = null ;
}
} // Array to store the recent visited // node at particular level represented // by indices let a= new Array(100);
// Function to connect nodes using preorder // traversal function connectNodes(p,l)
{ if (p == null )
return ;
// assigning left neighbor
p.leftNeighbour = a[l];
// updating value of the recent
// node at level
a[l] = p;
connectNodes(p.left, l + 1);
connectNodes(p.right, l + 1);
} // Utility function to connect nodes to neighbours // using preorder traversal function connectNodesUtil(root)
{ // Initialize nodes at every level to null
for (let i = 0; i < 100; i++)
a[i] = new node(-1);
// Populates next left pointer in all nodes
connectNodes(root, 0);
// Let us check the values of next left pointers
document.write( "Following are populated leftNeighbour" +
" pointers in the tree:<br>" );
document.write( "leftNeighbour of " + root.data +
" is " + (root.leftNeighbour != null ?
root.leftNeighbour.data : -1)+ "<br>" );
document.write( "leftNeighbour of " + root.left.data +
" is " + (root.left.leftNeighbour != null ?
root.left.leftNeighbour.data : -1)+ "<br>" );
document.write( "leftNeighbour of " + root.right.data +
" is " + (root.right.leftNeighbour != null ?
root.right.leftNeighbour.data : -1) + "<br>" );
document.write( "leftNeighbour of " + root.left.left.data +
" is " + (root.left.left.leftNeighbour != null ?
root.left.left.leftNeighbour.data : -1)+ "<br>" );
} // Driver Code /* Constructed binary tree is 10
/ \
8 2
/
3
*/
let root = new node(10);
root.left = new node(8);
root.right = new node(2);
root.left.left = new node(3);
connectNodesUtil(root);
// This code is contributed by patel2127 </script> |
Following are populated leftNeighbour pointers in the tree: leftNeighbour of 10 is -1 leftNeighbour of 8 is -1 leftNeighbour of 2 is 8 leftNeighbour of 3 is -1