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

• Difficulty Level : Basic
• Last Updated : 12 Jan, 2023

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

To check if a binary tree has duplicate values, you can follow these steps:

1. Create a set to store the values that have been encountered so far.
2. Start a traversal of the binary tree. For each node, check if its value is in the set. If it is, return true to indicate that the tree contains duplicate values. If it is not, add the value to the set and continue the traversal.
3. When the traversal is complete, return false to indicate that no duplicate values were found.

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 ``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 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 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

 ``

Output

`Yes`

## Java

 `import` `java.util.HashSet;` `class` `Node {``  ``int` `data;``  ``Node left;``  ``Node right;` `  ``public` `Node(``int` `data) {``    ``this``.data = data;``  ``}``}` `class` `BinaryTree {``  ``Node root;` `  ``public` `boolean` `hasDuplicateValues() {``    ``HashSet values = ``new` `HashSet<>();``    ``return` `hasDuplicateValues(root, values);``  ``}` `  ``private` `boolean` `hasDuplicateValues(Node focusNode, HashSet values) {``    ``if` `(focusNode == ``null``) {``      ``return` `false``;``    ``}` `    ``if` `(values.contains(focusNode.data)) {``      ``return` `true``;``    ``}` `    ``values.add(focusNode.data);``    ``return` `hasDuplicateValues(focusNode.left, values) || hasDuplicateValues(focusNode.right, values);``  ``}``}` `public` `class` `Main {``  ``public` `static` `void` `main(String[] args) {``    ``BinaryTree tree = ``new` `BinaryTree();` `    ``tree.root = ``new` `Node(``1``);``    ``tree.root.left = ``new` `Node(``2``);``    ``tree.root.right = ``new` `Node(``2``);` `    ``System.out.println(tree.hasDuplicateValues()); ``// prints "true"` `    ``tree.root.right = ``new` `Node(``3``);` `    ``System.out.println(tree.hasDuplicateValues()); ``// prints "false"``  ``}``}`

Output

```true
false```

Complexity analysis:

The hasDuplicateValues method has a time complexity of O(n), where n is the number of nodes in the binary tree. This is because the method visits each node exactly once in order to check if it has already been seen before.

The space complexity of the hasDuplicateValues method is O(m), where m is the number of unique values in the binary tree. The HashSet values stores all the unique values that have been seen so far, and its size can at most be equal to the number of unique values in the binary tree. This is because if there are no duplicates in the tree, the size of the HashSet will be equal to the number of nodes in the tree, which is n.
Otherwise, if there are duplicates, the size of the set will be less than the number of nodes, hence m<=n.

In the worst-case scenario, where all the values in the tree are different, the space complexity of the method would be O(n). In the best-case scenario, where all the values in the tree are the same, the space complexity of the method would be O(1).

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