Related Articles

# 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 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 nodeNode* 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 treevoid 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 rootint 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 methodsint 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 nodeclass newNode:    def __init__(self, data):        self.data = data        self.left = self.right = None # Utility method to return length of# longest consecutive sequence of treedef 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 rootdef 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 Codeif __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 treeusing 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



Output:

3