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# Top three elements in binary tree

• Difficulty Level : Easy
• Last Updated : 30 Jun, 2021

We have a simple binary tree and we have to print the top 3 largest elements present in the binary tree.
Examples:

```Input :
1
/  \
2    3
/ \   / \
4  5   4  5
Output :Three largest elements are 5 4 3```

Approach We can simply take three variables first, second, third to store the first largest, second largest, third largest respectively and perform preorder traversal and each time we will update the elements accordingly.
This approach will take O(n) time only.
Algorithm-

```1- Take 3 variables first, second, third
2- Perform a preorder traversal
if (root==NULL)
return
if root's data is larger then first
update third with second
second with first
first with root's data
else if root's data is larger then
second and not equal to first
update third with second
second with root's data
else if root's data is larger then
third and not equal to first &
second
update third with root's data
3- call preorder for root->left
4- call preorder for root->right```

## C++

 `// CPP program to find largest three elements in``// a binary tree.``#include ``using` `namespace` `std;` `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 = NULL;``  ``node->right = NULL;``  ``return` `(node);``}` `// function to find three largest element``void` `threelargest(Node *root, ``int` `&first, ``int` `&second,``                                          ``int` `&third) {``  ``if` `(root == NULL)``    ``return``;` `  ``// if data is greater than first large number``  ``// update the top three list``  ``if` `(root->data > first) {``    ``third = second;``    ``second = first;``    ``first = root->data;``  ``}` `  ``// if data is greater than second large number``  ``// and not equal to first update the bottom``  ``// two list``  ``else` `if` `(root->data > second && root->data != first) {``    ``third = second;``    ``second = root->data;``  ``}` `  ``// if data is greater than third large number``  ``// and not equal to first & second update the``  ``// third highest list``  ``else` `if` `(root->data > third &&``           ``root->data != first &&``           ``root->data != second)``    ``third = root->data;` `  ``threelargest(root->left, first, second, third);``  ``threelargest(root->right, first, second, third);``}` `// driver function``int` `main() {``  ``struct` `Node *root = newNode(1);``  ``root->left = newNode(2);``  ``root->right = newNode(3);``  ``root->left->left = newNode(4);``  ``root->left->right = newNode(5);``  ``root->right->left = newNode(4);``  ``root->right->right = newNode(5);` `  ``int` `first = 0, second = 0, third = 0;``  ``threelargest(root, first, second, third);``  ``cout << ``"three largest elements are "``       ``<< first << ``" "` `<< second << ``" "``       ``<< third;``  ``return` `0;``}`

## Java

 `// Java program to find largest three elements``// in a binary tree.``import` `java.util.*;` `class` `GFG``{``static` `class` `Node``{``    ``int` `data;``    ``Node left;``    ``Node right;``};` `static` `int` `first, second, third;` `/* Helper function that allocates``a new Node with the given data and``null left and right pointers. */``static` `Node newNode(``int` `data)``{``    ``Node node = ``new` `Node();``    ``node.data = data;``    ``node.left = ``null``;``    ``node.right = ``null``;``    ``return` `(node);``}` `// function to find three largest element``static` `void` `threelargest(Node root)``{``if` `(root == ``null``)``    ``return``;` `// if data is greater than first large number``// update the top three list``if` `(root.data > first)``{``    ``third = second;``    ``second = first;``    ``first = root.data;``}` `// if data is greater than second large number``// and not equal to first update the bottom``// two list``else` `if` `(root.data > second &&``         ``root.data != first)``{``    ``third = second;``    ``second = root.data;``}` `// if data is greater than third large number``// and not equal to first & second update the``// third highest list``else` `if` `(root.data > third &&``         ``root.data != first &&``         ``root.data != second)``    ``third = root.data;` `threelargest(root.left);``threelargest(root.right);``}` `// driver function``public` `static` `void` `main(String[] args)``{``    ``Node root = newNode(``1``);``    ``root.left = newNode(``2``);``    ``root.right = newNode(``3``);``    ``root.left.left = newNode(``4``);``    ``root.left.right = newNode(``5``);``    ``root.right.left = newNode(``4``);``    ``root.right.right = newNode(``5``);``    ` `    ``first = ``0``; second = ``0``; third = ``0``;``    ``threelargest(root);``    ``System.out.print(``"three largest elements are "` `+``                      ``first + ``" "` `+ second + ``" "` `+ third);``}``}` `// This code is contributed by PrinciRaj1992`

## Python3

 `# Python3 program to find largest three``# elements in a binary tree.` `# Helper function that allocates a new``# Node with the given data and None``# left and right pointers.``class` `newNode:``  ``def` `__init__(``self``, data):``      ``self``.data ``=` `data``      ``self``.left ``=` `None``      ``self``.right ``=` `None``  ` `# function to find three largest element``def` `threelargest(root, first, second, third):``  ``if` `(root ``=``=` `None``):``    ``return``   ` `  ``# if data is greater than first large``  ``# number update the top three list``  ``if` `(root.data > first[``0``]):``    ``third[``0``] ``=` `second[``0``]``    ``second[``0``] ``=` `first[``0``]``    ``first[``0``] ``=` `root.data``   ` `  ``# if data is greater than second large``  ``# number and not equal to first update``  ``# the bottom two list``  ``elif` `(root.data > second[``0``] ``and``        ``root.data !``=` `first[``0``]):``    ``third[``0``] ``=` `second[``0``]``    ``second[``0``] ``=` `root.data``   ` `  ``# if data is greater than third large``  ``# number and not equal to first & second``  ``# update the third highest list``  ``elif` `(root.data > third[``0``] ``and``        ``root.data !``=` `first[``0``] ``and``        ``root.data !``=` `second[``0``]):``      ``third[``0``] ``=` `root.data``   ` `  ``threelargest(root.left, first,``                  ``second, third)``  ``threelargest(root.right, first,``                   ``second, third)` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:` `    ``root ``=` `newNode(``1``)``    ``root.left ``=` `newNode(``2``)``    ``root.right ``=` `newNode(``3``)``    ``root.left.left ``=` `newNode(``4``)``    ``root.left.right ``=` `newNode(``5``)``    ``root.right.left ``=` `newNode(``4``)``    ``root.right.right ``=` `newNode(``5``)``    ` `    ``first ``=` `[``0``]``    ``second ``=` `[``0``]``    ``third ``=` `[``0``]``    ``threelargest(root, first, second, third)``    ``print``(``"three largest elements are"``,``           ``first[``0``], second[``0``], third[``0``])` `# This code is contributed by PranchalK`

## C#

 `// C# program to find largest three elements``// in a binary tree.``using` `System;``class` `GFG``{``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node left;``    ``public` `Node right;``};` `static` `int` `first, second, third;` `/* Helper function that allocates``a new Node with the given data and``null left and right pointers. */``static` `Node newNode(``int` `data)``{``    ``Node node = ``new` `Node();``    ``node.data = data;``    ``node.left = ``null``;``    ``node.right = ``null``;``    ``return` `(node);``}` `// function to find three largest element``static` `void` `threelargest(Node root)``{``    ``if` `(root == ``null``)``        ``return``;``    ` `    ``// if data is greater than first large number``    ``// update the top three list``    ``if` `(root.data > first)``    ``{``        ``third = second;``        ``second = first;``        ``first = root.data;``    ``}``    ` `    ``// if data is greater than second large number``    ``// and not equal to first update the bottom``    ``// two list``    ``else` `if` `(root.data > second &&``             ``root.data != first)``    ``{``        ``third = second;``        ``second = root.data;``    ``}``    ` `    ``// if data is greater than third large number``    ``// and not equal to first & second update the``    ``// third highest list``    ``else` `if` `(root.data > third &&``             ``root.data != first &&``             ``root.data != second)``        ``third = root.data;``    ` `    ``threelargest(root.left);``    ``threelargest(root.right);``}` `// Driver Code``public` `static` `void` `Main(String[] args)``{``    ``Node root = newNode(1);``    ``root.left = newNode(2);``    ``root.right = newNode(3);``    ``root.left.left = newNode(4);``    ``root.left.right = newNode(5);``    ``root.right.left = newNode(4);``    ``root.right.right = newNode(5);``    ` `    ``first = 0; second = 0; third = 0;``    ``threelargest(root);``    ``Console.WriteLine(``"three largest elements are "` `+``                       ``first + ``" "` `+ second + ``" "` `+ third);``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``
Output:
`three largest elements are 5 4 3`

Time Complexity: O(N)

Auxiliary Space: O(1)

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