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Binary Tree (Array implementation)
• Difficulty Level : Easy
• Last Updated : 08 Sep, 2020

Talking about representation, trees can be represented in two ways:
1) Dynamic Node Representation (Linked Representation).
2) Array Representation (Sequential Representation).
We are going to talk about the sequential representation of the trees.
To represent tree using an array, the numbering of nodes can start either from 0–(n-1) or 1– n.

```       A(0)
/   \
B(1)  C(2)
/   \      \
D(3)  E(4)   F(6)
OR,
A(1)
/   \
B(2)  C(3)
/   \      \
D(4)  E(5)   F(7)

```

For first case(0—n-1),
if (say)father=p;
then left_son=(2*p)+1;
and right_son=(2*p)+2;
For second case(1—n),
if (say)father=p;
then left_son=(2*p);
and right_son=(2*p)+1;
where father, left_son and right_son are the values of indices of the array.

## C++

 `// C++ implementation of tree using array``// numbering starting from 0 to n-1.``#include``using` `namespace` `std;``char` `tree;``int` `root(``char` `key)``{``    ``if``(tree != ``'\0'``)``        ``cout << ``"Tree already had root"``;``    ``else``        ``tree = key;``    ``return` `0;``}` `int` `set_left(``char` `key, ``int` `parent)``{``    ``if``(tree[parent] == ``'\0'``)``        ``cout << ``"\nCan't set child at"``             ``<< (parent * 2) + 1``             ``<< ``" , no parent found"``;``    ``else``        ``tree[(parent * 2) + 1] = key;``    ``return` `0;``}` `int` `set_right(``char` `key, ``int` `parent)``{``    ``if``(tree[parent] == ``'\0'``)``        ``cout << ``"\nCan't set child at"``             ``<< (parent * 2) + 2``             ``<< ``" , no parent found"``;``    ``else``        ``tree[(parent * 2) + 2] = key;``    ``return` `0;``}` `int` `print_tree()``{``    ``cout << ``"\n"``;``    ``for``(``int` `i = 0; i < 10; i++)``    ``{``        ``if``(tree[i] != ``'\0'``)``            ``cout << tree[i];``        ``else``            ``cout << ``"-"``;``    ``}``    ``return` `0;``}` `// Driver Code``int` `main()``{``    ``root(``'A'``);``    ``//insert_left('B',0);``    ``set_right(``'C'``, 0);``    ``set_left(``'D'``, 1);``    ``set_right(``'E'``, 1);``    ``set_right(``'F'``, 2);``    ``print_tree();``    ``return` `0;``}` `// This code is contributed by``// Gaurav_Kumar_Raghav`

## Java

 `// JAVA implementation of tree using array``// numbering starting from 0 to n-1.``import` `java.util.*;``import` `java.lang.*;``import` `java.io.*;` `class` `Tree {``    ``public` `static` `void` `main(String[] args)``    ``{``        ``Array_imp obj = ``new` `Array_imp();``        ``obj.Root(``"A"``);``        ``// obj.set_Left("B", 0);``        ``obj.set_Right(``"C"``, ``0``);``        ``obj.set_Left(``"D"``, ``1``);``        ``obj.set_Right(``"E"``, ``1``);``        ``obj.set_Left(``"F"``, ``2``);``        ``obj.print_Tree();``    ``}``}` `class` `Array_imp {``    ``static` `int` `root = ``0``;``    ``static` `String[] str = ``new` `String[``10``];` `    ``/*create root*/``    ``public` `void` `Root(String key)``    ``{``        ``str[``0``] = key;``    ``}` `    ``/*create left son of root*/``    ``public` `void` `set_Left(String key, ``int` `root)``    ``{``        ``int` `t = (root * ``2``) + ``1``;` `        ``if` `(str[root] == ``null``) {``            ``System.out.printf(``"Can't set child at %d, no parent found\n"``, t);``        ``}``        ``else` `{``            ``str[t] = key;``        ``}``    ``}` `    ``/*create right son of root*/``    ``public` `void` `set_Right(String key, ``int` `root)``    ``{``        ``int` `t = (root * ``2``) + ``2``;` `        ``if` `(str[root] == ``null``) {``            ``System.out.printf(``"Can't set child at %d, no parent found\n"``, t);``        ``}``        ``else` `{``            ``str[t] = key;``        ``}``    ``}` `    ``public` `void` `print_Tree()``    ``{``        ``for` `(``int` `i = ``0``; i < ``10``; i++) {``            ``if` `(str[i] != ``null``)``                ``System.out.print(str[i]);``            ``else``                ``System.out.print(``"-"``);``        ``}``    ``}``}`

## C#

 `// C# implementation of tree using array``// numbering starting from 0 to n-1.``using` `System;` `public` `class` `Tree {``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``Array_imp obj = ``new` `Array_imp();``        ``obj.Root(``"A"``);``        ``// obj.set_Left("B", 0);``        ``obj.set_Right(``"C"``, 0);``        ``obj.set_Left(``"D"``, 1);``        ``obj.set_Right(``"E"``, 1);``        ``obj.set_Left(``"F"``, 2);``        ``obj.print_Tree();``    ``}``}` `class` `Array_imp {``    ``static` `int` `root = 0;``    ``static` `String[] str = ``new` `String;` `    ``/*create root*/``    ``public` `void` `Root(String key)``    ``{``        ``str = key;``    ``}` `    ``/*create left son of root*/``    ``public` `void` `set_Left(String key, ``int` `root)``    ``{``        ``int` `t = (root * 2) + 1;` `        ``if` `(str[root] == ``null``) {``            ``Console.Write(``"Can't set child at {0}, no parent found\n"``, t);``        ``}``        ``else` `{``            ``str[t] = key;``        ``}``    ``}` `    ``/*create right son of root*/``    ``public` `void` `set_Right(String key, ``int` `root)``    ``{``        ``int` `t = (root * 2) + 2;` `        ``if` `(str[root] == ``null``) {``            ``Console.Write(``"Can't set child at {0}, no parent found\n"``, t);``        ``}``        ``else` `{``            ``str[t] = key;``        ``}``    ``}` `    ``public` `void` `print_Tree()``    ``{``        ``for` `(``int` `i = 0; i < 10; i++) {``            ``if` `(str[i] != ``null``)``                ``Console.Write(str[i]);``            ``else``                ``Console.Write(``"-"``);``        ``}``    ``}``}` `// This code contributed by Rajput-Ji`

## Python3

 `# Python3 implementation of tree using array``# numbering starting from 0 to n-1.``tree ``=` `[``None``] ``*` `10`  `def` `root(key):``    ``if` `tree[``0``] !``=` `None``:``        ``print``(``"Tree already had root"``)``    ``else``:``        ``tree[``0``] ``=` `key`  `def` `set_left(key, parent):``    ``if` `tree[parent] ``=``=` `None``:``        ``print``(``"Can't set child at"``, (parent ``*` `2``) ``+` `1``, ``", no parent found"``)``    ``else``:``        ``tree[(parent ``*` `2``) ``+` `1``] ``=` `key`  `def` `set_right(key, parent):``    ``if` `tree[parent] ``=``=` `None``:``        ``print``(``"Can't set child at"``, (parent ``*` `2``) ``+` `2``, ``", no parent found"``)``    ``else``:``        ``tree[(parent ``*` `2``) ``+` `2``] ``=` `key`  `def` `print_tree():``    ``for` `i ``in` `range``(``10``):``        ``if` `tree[i] !``=` `None``:``            ``print``(tree[i], end``=``"")``        ``else``:``            ``print``(``"-"``, end``=``"")``    ``print``()`  `# Driver Code``root(``'A'``)``set_right(``'C'``, ``0``)``set_left(``'D'``, ``1``)``set_right(``'E'``, ``1``)``set_right(``'F'``, ``2``)``print_tree()` `# This code is contributed by Gaurav Kumar Tailor`

Output:

```Can't set child at 3, no parent found
Can't set child at 4, no parent found
A-C---F---

```

Note – Please refer this if you want to construct tree from the given parent array.

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