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Binary Tree (Array implementation)

Talking about representation, trees can be represented in two way:
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, 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.



Code –

// 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 ",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 ",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("-");
              
        }
    }
}

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.



This article is attributed to GeeksforGeeks.org

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