将所有节点连接到二叉树中的左邻居
给定一个二叉树，其中每个节点都包含一个额外的空指针，最初为空。任务是使用这个额外的指针将二叉树的所有节点连接到同一级别的左邻居。
例子：
Input :
A
/ \
B C
/ \ \
D E F
Output :
NULL<--A
/ \
NULL<--B<--C
/ \ \
NULL<--D<--E<--F方法：
我们可以使用树的前序遍历在每次调用时传递节点的级别。根节点位于级别 0。在遍历时，我们将最近在该级别看到的节点存储在节点指针数组中。前序遍历确保数组中特定级别的节点是即将到来的同一级别节点的左邻居。
下面是上述方法的实现：
C++
// CPP program to connect nodes
// at same level using extended
// pre-order traversal
#include
#include
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
// 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 KunduPython3
# 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 29C#
// 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 avanitrachhadiya2155Javascript
输出：
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