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Longest consecutive sequence in Binary tree

  • Difficulty Level : Medium
  • Last Updated : 16 Jun, 2021

Given a Binary Tree find the length of the longest path which comprises of nodes with consecutive values in increasing order. Every node is considered as a path of length 1.
Examples: 
 

In below diagram binary tree with longest consecutive path(LCP) are shown :

We can solve above problem recursively. At each node we need information of its parent node, if current node has value one more than its parent node then it makes a consecutive path, at each node we will compare node’s value with its parent value and update the longest consecutive path accordingly. 
For getting the value of parent node, we will pass the (node_value + 1) as an argument to the recursive method and compare the node value with this argument value, if satisfies, update the current length of consecutive path otherwise reinitialize current path length by 1. 
Please see below code for better understanding : 
 

C++




// C/C++ program to find longest consecutive
// sequence in binary tree
#include <bits/stdc++.h>
using namespace std;
 
/* A binary tree node has data, pointer to left
   child and a pointer to right child */
struct Node
{
    int data;
    Node *left, *right;
};
 
// A utility function to create a node
Node* newNode(int data)
{
    Node* temp = new Node;
    temp->data = data;
    temp->left = temp->right = NULL;
    return temp;
}
 
// Utility method to return length of longest
// consecutive sequence of tree
void longestConsecutiveUtil(Node* root, int curLength,
                              int expected, int& res)
{
    if (root == NULL)
        return;
 
    // if root data has one more than its parent
    // then increase current length
    if (root->data == expected)
        curLength++;
    else
        curLength = 1;
 
    //  update the maximum by current length
    res = max(res, curLength);
 
    // recursively call left and right subtree with
    // expected value 1 more than root data
    longestConsecutiveUtil(root->left, curLength,
                           root->data + 1, res);
    longestConsecutiveUtil(root->right, curLength,
                           root->data + 1, res);
}
 
// method returns length of longest consecutive
// sequence rooted at node root
int longestConsecutive(Node* root)
{
    if (root == NULL)
        return 0;
 
    int res = 0;
 
    //  call utility method with current length 0
    longestConsecutiveUtil(root, 0, root->data, res);
 
    return res;
}
 
//  Driver code to test above methods
int main()
{
    Node* root = newNode(6);
    root->right = newNode(9);
    root->right->left = newNode(7);
    root->right->right = newNode(10);
    root->right->right->right = newNode(11);
 
    printf("%d\n", longestConsecutive(root));
    return 0;
}

Java




// Java program to find longest consecutive
// sequence in binary tree
 
class Node
{
    int data;
    Node left, right;
 
    Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
class Result
{
    int res = 0;
}
 
class BinaryTree
{
    Node root;
 
    // method returns length of longest consecutive
    // sequence rooted at node root
    int longestConsecutive(Node root)
    {
        if (root == null)
            return 0;
 
        Result res = new Result();
         
        // call utility method with current length 0
        longestConsecutiveUtil(root, 0, root.data, res);
         
        return res.res;
    }
 
    // Utility method to return length of longest
    // consecutive sequence of tree
    private void longestConsecutiveUtil(Node root, int curlength,
                                        int expected, Result res)
    {
        if (root == null)
            return;
 
        // if root data has one more than its parent
        // then increase current length
        if (root.data == expected)
            curlength++;
        else
            curlength = 1;
 
        // update the maximum by current length
        res.res = Math.max(res.res, curlength);
 
        // recursively call left and right subtree with
        // expected value 1 more than root data
        longestConsecutiveUtil(root.left, curlength, root.data + 1, res);
        longestConsecutiveUtil(root.right, curlength, root.data + 1, res);
    }
 
    // Driver code
    public static void main(String args[])
    {
        BinaryTree tree = new BinaryTree();
 
        tree.root = new Node(6);
        tree.root.right = new Node(9);
        tree.root.right.left = new Node(7);
        tree.root.right.right = new Node(10);
        tree.root.right.right.right = new Node(11);
 
        System.out.println(tree.longestConsecutive(tree.root));
    }
}
 
// This code is contributed by shubham96301

Python3




# Python3 program to find longest consecutive
# sequence in binary tree
 
# A utility class to create a node
class newNode:
    def __init__(self, data):
        self.data = data
        self.left = self.right = None
 
# Utility method to return length of
# longest consecutive sequence of tree
def longestConsecutiveUtil(root, curLength,
                           expected, res):
    if (root == None):
        return
 
    # if root data has one more than its
    # parent then increase current length
    if (root.data == expected):
        curLength += 1
    else:
        curLength = 1
 
    # update the maximum by current length
    res[0] = max(res[0], curLength)
 
    # recursively call left and right subtree
    # with expected value 1 more than root data
    longestConsecutiveUtil(root.left, curLength,
                           root.data + 1, res)
    longestConsecutiveUtil(root.right, curLength,
                           root.data + 1, res)
 
# method returns length of longest consecutive
# sequence rooted at node root
def longestConsecutive(root):
    if (root == None):
        return 0
 
    res = [0]
 
    # call utility method with current length 0
    longestConsecutiveUtil(root, 0, root.data, res)
 
    return res[0]
 
# Driver Code
if __name__ == '__main__':
 
    root = newNode(6)
    root.right = newNode(9)
    root.right.left = newNode(7)
    root.right.right = newNode(10)
    root.right.right.right = newNode(11)
 
    print(longestConsecutive(root))
 
# This code is contributed by PranchalK

C#




// C# program to find longest consecutive
// sequence in binary tree
using System;
class Node
{
    public int data;
    public Node left, right;
 
    public Node(int item)
    {
        data = item;
        left = right = null;
    }
}
 
class Result
{
    public int res = 0;
}
 
class GFG
{
    Node root;
 
    // method returns length of longest consecutive
    // sequence rooted at node root
    int longestConsecutive(Node root)
    {
        if (root == null)
            return 0;
 
        Result res = new Result();
         
        // call utility method with current length 0
        longestConsecutiveUtil(root, 0, root.data, res);
         
        return res.res;
    }
 
    // Utility method to return length of longest
    // consecutive sequence of tree
    private void longestConsecutiveUtil(Node root, int curlength,
                                        int expected, Result res)
    {
        if (root == null)
            return;
 
        // if root data has one more than its parent
        // then increase current length
        if (root.data == expected)
            curlength++;
        else
            curlength = 1;
 
        // update the maximum by current length
        res.res = Math.Max(res.res, curlength);
 
        // recursively call left and right subtree with
        // expected value 1 more than root data
        longestConsecutiveUtil(root.left, curlength,
                               root.data + 1, res);
        longestConsecutiveUtil(root.right, curlength,
                               root.data + 1, res);
    }
 
    // Driver code
    public static void Main(String []args)
    {
        GFG tree = new GFG();
 
        tree.root = new Node(6);
        tree.root.right = new Node(9);
        tree.root.right.left = new Node(7);
        tree.root.right.right = new Node(10);
        tree.root.right.right.right = new Node(11);
 
        Console.WriteLine(tree.longestConsecutive(tree.root));
    }
}
 
// This code is contributed by 29AjayKumar

Javascript




<script>
 
// JavaScript program to find longest consecutive
// sequence in binary tree
 
class Node
{
    constructor(item)
    {
        this.data=item;
        this.left = this.right = null;
    }
}
 
let res = 0;
 
let root;
function longestConsecutive(root)
{
     if (root == null)
            return 0;
   
          res=[0];     
           
        // call utility method with current length 0
        longestConsecutiveUtil(root, 0, root.data, res);
           
        return res[0];
}
 
 // Utility method to return length of longest
    // consecutive sequence of tree
function longestConsecutiveUtil(root,curlength, expected,res)
{
    if (root == null)
            return;
   
        // if root data has one more than its parent
        // then increase current length
        if (root.data == expected)
            curlength++;
        else
            curlength = 1;
   
        // update the maximum by current length
        res[0] = Math.max(res[0], curlength);
   
        // recursively call left and right subtree with
        // expected value 1 more than root data
        longestConsecutiveUtil(root.left, curlength,
        root.data + 1, res);
        longestConsecutiveUtil(root.right, curlength,
        root.data + 1, res);
}
 
// Driver code
root = new Node(6);
root.right = new Node(9);
root.right.left = new Node(7);
root.right.right = new Node(10);
root.right.right.right = new Node(11);
 
document.write(longestConsecutive(root));
 
// This code is contributed by rag2127
 
</script>

Output:  

3



Also discussed on below link: 
Maximum Consecutive Increasing Path Length in Binary Tree
This article is contributed by Utkarsh Trivedi. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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