Diagonal Traversal of Binary Tree

3.5

Consider lines of slope -1 passing between nodes. Given a Binary Tree, print all diagonal elements in a binary tree belonging to same line.

Input : Root of below tree
unnamed

Output : 
Diagonal Traversal of binary tree : 
 8 10 14
 3 6 7 13
 1 4

The idea is to use map. We use different slope distances and use them as key in map. Value in map is vector (or dynamic array) of nodes. We traverse the tree to store values in map. Once map is built, we print contents of it.

Below is C++ implementation of above idea.

C++

// C++ program for diagnoal traversal of Binary Tree
#include <bits/stdc++.h>
using namespace std;

// Tree node
struct Node
{
    int data;
    Node *left, *right;
};

/* root - root of the binary tree
   d -  distance of current line from rightmost
        -topmost slope.
   diagonalPrint - multimap to store Diagonal
                   elements (Passed by Reference) */
void diagonalPrintUtil(Node* root, int d,
                      map<int, vector<int>> &diagonalPrint)
{
    // Base case
    if (!root)
        return;

    // Store all nodes of same line together as a vector
    diagonalPrint[d].push_back(root->data);

    // Increase the vertical distance if left child
    diagonalPrintUtil(root->left, d + 1, diagonalPrint);

    // Vertical distance remains same for right child
    diagonalPrintUtil(root->right, d, diagonalPrint);
}

// Print diagonal traversal of given binary tree
void diagonalPrint(Node* root)
{
    // create a map of vectors to store Diagonal elements
    map<int, vector<int> > diagonalPrint;
    diagonalPrintUtil(root, 0, diagonalPrint);

    cout << "Diagonal Traversal of binary tree : n";
    for (auto it = diagonalPrint.begin();
         it != diagonalPrint.end(); ++it)
    {
        for (auto itr = it->second.begin();
             itr != it->second.end(); ++itr)
            cout << *itr  << ' ';

        cout << 'n';
    }
}

// Utility method to create a new node
Node* newNode(int data)
{
    Node* node = new Node;
    node->data = data;
    node->left = node->right = NULL;
    return node;
}

// Driver program
int main()
{
    Node* root = newNode(8);
    root->left = newNode(3);
    root->right = newNode(10);
    root->left->left = newNode(1);
    root->left->right = newNode(6);
    root->right->right = newNode(14);
    root->right->right->left = newNode(13);
    root->left->right->left = newNode(4);
    root->left->right->right = newNode(7);

    /*  Node* root = newNode(1);
        root->left = newNode(2);
        root->right = newNode(3);
        root->left->left = newNode(9);
        root->left->right = newNode(6);
        root->right->left = newNode(4);
        root->right->right = newNode(5);
        root->right->left->right = newNode(7);
        root->right->left->left = newNode(12);
        root->left->right->left = newNode(11);
        root->left->left->right = newNode(10);*/

    diagonalPrint(root);

    return 0;
}

Java

// Java program for diagonal traversal of Binary Tree
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Vector;

public class DiagonalTraversalBTree 
{
    // Tree node
    static class Node{
        int data;
        Node left;
        Node right;
        
        //constructor
        Node(int data)
        {
            this.data=data;
            left = null;
            right =null;
        }
    }
    
    /* root - root of the binary tree
       d -  distance of current line from rightmost
            -topmost slope.
       diagonalPrint - HashMap to store Diagonal
                       elements (Passed by Reference) */
    static void diagonalPrintUtil(Node root,int d,
            HashMap<Integer,Vector<Integer>> diagonalPrint){
        
         // Base case
        if (root == null)
            return;
        
        // get the list at the particular d value
        Vector<Integer> k = diagonalPrint.get(d);
        
        // k is null then create a vector and store the data
        if (k == null)
        {
            k = new Vector<>();
            k.add(root.data);
        }
        
        // k is not null then update the list
        else
        {
            k.add(root.data);
        }
        
        // Store all nodes of same line together as a vector
        diagonalPrint.put(d,k);
        
        // Increase the vertical distance if left child
        diagonalPrintUtil(root.left, d + 1, diagonalPrint);
         
        // Vertical distance remains same for right child
        diagonalPrintUtil(root.right, d, diagonalPrint);
    }
    
    // Print diagonal traversal of given binary tree
    static void diagonalPrint(Node root)
    {
        // create a map of vectors to store Diagonal elements
        HashMap<Integer,Vector<Integer>> diagonalPrint = new HashMap<>();
        diagonalPrintUtil(root, 0, diagonalPrint);
        
        System.out.println("Diagonal Traversal of Binnary Tree");
        for (Entry<Integer, Vector<Integer>> entry : diagonalPrint.entrySet())
        {
            System.out.println(entry.getValue());
        }
    }
    
    // Driver program
    public static void main(String[] args) {
        
        Node root = new Node(8);
        root.left = new Node(3);
        root.right = new Node(10);
        root.left.left = new Node(1);
        root.left.right = new Node(6);
        root.right.right = new Node(14);
        root.right.right.left = new Node(13);
        root.left.right.left = new Node(4);
        root.left.right.right = new Node(7);
        
        diagonalPrint(root);
    }
}
// This code is contributed by Sumit Ghosh

Python


# Python program for diagonal traversal of Binary Tree

# A binary tree node
class Node:

    # Constructor to create a new binary tree node
    def __init__(self, data):
        self.data = data 
        self.left = None
        self.right = None


""" root - root of the binary tree
   d -  distance of current line from rightmost
        -topmost slope.
   diagonalPrint - multimap to store Diagonal
                   elements (Passed by Reference) """
def diagonalPrintUtil(root, d, diagonalPrintMap):
    
    # Base Case 
    if root is None:
        return 

    # Store all nodes of same line together as a vector
    try :
        diagonalPrintMap[d].append(root.data)
    except KeyError:
        diagonalPrintMap[d] = [root.data]

    # Increase the vertical distance if left child
    diagonalPrintUtil(root.left, d+1, diagonalPrintMap)
    
    # Vertical distance remains same for right child
    diagonalPrintUtil(root.right, d, diagonalPrintMap)



# Print diagonal traversal of given binary tree
def diagonalPrint(root):

    # Create a dict to store diagnoal elements 
    diagonalPrintMap = dict()
    
    # Find the diagonal traversal
    diagonalPrintUtil(root, 0, diagonalPrintMap)

    print "Diagonal Traversal of binary tree : "
    for i in diagonalPrintMap:
        for j in diagonalPrintMap[i]:
            print j,
        print ""


# Driver Program 
root = Node(8)
root.left = Node(3)
root.right = Node(10)
root.left.left = Node(1)
root.left.right = Node(6)
root.right.right = Node(14)
root.right.right.left = Node(13)
root.left.right.left = Node(4)
root.left.right.right = Node(7)

diagonalPrint(root)

# This code is contributed by Nikhil Kumar Singh(nickzuck_007)


Output :
Diagonal Traversal of binary tree : 
 8 10 14
 3 6 7 13
 1 4

This article is contributed by Aditya Goel. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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