Check if a Binary Tree (not BST) has duplicate values

Check if a Binary Tree (not BST) has duplicate values

Examples: 

Input : Root of below tree
         1
       /   \
      2     3
             \
              2
Output : Yes
Explanation : The duplicate value is 2.

Input : Root of below tree
         1
       /   \
     20     3
             \
              4
Output : No
Explanation : There are no duplicates.

A simple solution is to store inorder traversal of given binary tree in an array. Then check if array has duplicates or not. We can avoid the use of array and solve the problem in O(n) time. The idea is to use hashing. We traverse the given tree, for every node, we check if it already exists in hash table. If exists, we return true (found duplicate). If it does not exist, we insert into hash table.

Implementation:

C++

// C++ Program to check duplicates
// 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;
    struct Node* left;
    struct Node* right;
};

// Helper function that allocates
// a new Node with the given data
// and NULL left and right pointers.
struct Node* newNode(int data)
{
    struct Node* node = new Node;
    node->data = data;
    node->left = node->right = NULL;
    return (node);
}

bool checkDupUtil(Node* root, unordered_set<int> &s)
{
    // If tree is empty, there are no
    // duplicates.
    if (root == NULL)
       return false;

    // If current node's data is already present.
    if (s.find(root->data) != s.end())
       return true;

    // Insert current node
    s.insert(root->data);

    // Recursively check in left and right
    // subtrees.
    return checkDupUtil(root->left, s) ||
           checkDupUtil(root->right, s);
}

// To check if tree has duplicates
bool checkDup(struct Node* root)
{
    unordered_set<int> s;
    return checkDupUtil(root, s);
}

// Driver program to test above functions
int main()
{
    struct Node* root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(2);
    root->left->left = newNode(3);
    if (checkDup(root))
        printf("Yes");
    else
        printf("No");

    return 0;
}

Java

// Java Program to check duplicates
// in Binary Tree
import java.util.HashSet;
public class CheckDuplicateValues {

    //Function that used HashSet to find presence of duplicate nodes
    public static boolean checkDupUtil(Node root, HashSet<Integer> s)
    {
        // If tree is empty, there are no
        // duplicates.
        if (root == null)
            return false;

        // If current node's data is already present.
        if (s.contains(root.data))
            return true;

        // Insert current node
        s.add(root.data);

        // Recursively check in left and right
        // subtrees.
        return checkDupUtil(root.left, s) || checkDupUtil(root.right, s);
    }

    // To check if tree has duplicates
    public static boolean checkDup(Node root)
    {
        HashSet<Integer> s=new HashSet<>();
        return checkDupUtil(root, s);
    }

    public static void main(String args[]) {
        Node root = new Node(1);
        root.left = new Node(2);
        root.right = new Node(2);
        root.left.left = new Node(3);
        if (checkDup(root))
            System.out.print("Yes");
        else
            System.out.print("No");
    }
}

// A binary tree Node has data,
// pointer to left child
// and a pointer to right child
class Node {
    int data;
    Node left,right;
    Node(int data)
    {
        this.data=data;
    }
};
//This code is contributed by Gaurav Tiwari

Python

""" Program to check duplicates
# in Binary Tree """

# Helper function that allocates a new
# node with the given data and None
# left and right pointers.
class newNode:

    # Construct to create a new node
    def __init__(self, key):
        self.data = key
        self.left = None
        self.right = None

def checkDupUtil( root, s) :

    # If tree is empty, there are no
    # duplicates.
    if (root == None) :
        return False

    # If current node's data is already present.
    if root.data in s:
        return True

    # Insert current node
    s.add(root.data)

    # Recursively check in left and right
    # subtrees.
    return checkDupUtil(root.left, s) or checkDupUtil(root.right, s)


# To check if tree has duplicates
def checkDup( root) :

    s=set()
    return checkDupUtil(root, s)


# Driver Code
if __name__ == '__main__':
    root = newNode(1)
    root.left = newNode(2)
    root.right = newNode(2)
    root.left.left = newNode(3)
    if (checkDup(root)):
        print("Yes")
    else:
        print("No")

# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

C#

// C# Program to check duplicates
// in Binary Tree
using System;
using System.Collections;
using System.Collections.Generic;

class CheckDuplicateValues
{

    //Function that used HashSet to
    // find presence of duplicate nodes
    public static Boolean checkDupUtil(Node root, HashSet<int> s)
    {
        // If tree is empty, there are no
        // duplicates.
        if (root == null)
            return false;

        // If current node's data is already present.
        if (s.Contains(root.data))
            return true;

        // Insert current node
        s.Add(root.data);

        // Recursively check in left and right
        // subtrees.
        return checkDupUtil(root.left, s) ||
                checkDupUtil(root.right, s);
    }

    // To check if tree has duplicates
    public static Boolean checkDup(Node root)
    {
        HashSet<int> s = new HashSet<int>();
        return checkDupUtil(root, s);
    }

    public static void Main(String []args)
    {
        Node root = new Node(1);
        root.left = new Node(2);
        root.right = new Node(2);
        root.left.left = new Node(3);
        if (checkDup(root))
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}

// A binary tree Node has data,
// pointer to left child
// and a pointer to right child
public class Node
{
    public int data;
    public Node left, right;
    public Node(int data)
    {
        this.data = data;
    }
};

// This code is contributed by Arnab Kundu

Javascript

<script>

    // JavaScript Program to check duplicates in Binary Tree

    class Node
    {
        constructor(data) {
           this.left = null;
           this.right = null;
           this.data = data;
        }
    }

    // Function that used HashSet to find
    // presence of duplicate nodes
    function checkDupUtil(root, s)
    {
        // If tree is empty, there are no
        // duplicates.
        if (root == null)
            return false;

        // If current node's data is already present.
        if (s.has(root.data))
            return true;

        // Insert current node
        s.add(root.data);

        // Recursively check in left and right
        // subtrees.
        return checkDupUtil(root.left, s) ||
        checkDupUtil(root.right, s);
    }

    // To check if tree has duplicates
    function checkDup(root)
    {
        let s = new Set();
        return checkDupUtil(root, s);
    }

    let root = new Node(1);
    root.left = new Node(2);
    root.right = new Node(2);
    root.left.left = new Node(3);
    if (checkDup(root))
      document.write("Yes");
    else
      document.write("No");

</script>

Output

Yes