C Program to construct binary tree from inorder and postorder

By | 13.04.2017

Construct tree from inorder and postorder


Write a C Program to construct binary tree from inorder and postorder. Here’s simple Program to construct binary tree from inorder and postorder in C Programming Language.


What is Tree ?


In linear data structure, data is organized in sequential order and in non-linear data structure, data is organized in random order. Tree is a very popular data structure used in wide range of applications.

A tree data structure can be defined as follows…

  • Tree is a non-linear data structure which organizes data in hierarchical structure and this is a recursive definition.

A tree data structure can also be defined as follows…

  • Tree data structure is a collection of data (Node) which is organized in hierarchical structure and this is a recursive definition.

Every individual element is called as Node. Node in a tree data structure, stores the actual data of that particular element and link to next element in hierarchical structure.


Below is the source code for C Program to construct binary tree from inorder and postorder which is successfully compiled and run on Windows System to produce desired output as shown below :


SOURCE CODE : :


/* C Program to construct binary tree from inorder and postorder */

#include<stdio.h>
#include<stdlib.h>

struct treenode
{
        int info;
        struct treenode *lchild;
        struct treenode *rchild;
}*root=NULL;

struct listnode
{
        struct listnode *prev;
        int info;
        struct listnode *next;
}*post=NULL, *in=NULL;

void display(struct treenode *ptr,int level);
struct listnode *addtoempty(struct listnode *start,int data);
struct listnode *addatend(struct listnode *start,int data);
struct listnode *create_list(struct listnode *start, int n);
struct treenode *construct(struct listnode *inptr,struct listnode *postptr, int num);
void inorder(struct treenode *ptr);
void preorder(struct treenode *ptr);
void postorder(struct treenode *ptr);

int main()
{
        int n;

        printf("Enter the number of nodes  :  ");
        scanf("%d",&n);

        printf("\nEnter inorder :\n");
        in = create_list(in,n);

        printf("\nEnter postorder:\n");
        post = create_list(post,n);

        root = construct(in,post,n);

        printf("\nInorder : ");  inorder(root);
        printf("\n\nPostorder : ");  postorder(root);
        printf("\n\nPreorder : "); preorder(root);
        printf("\n\n\nTree is : \n");
        display(root,0);
        printf("\n");

        return 0;

}/*End of main()*/

struct treenode *construct(struct listnode *inptr,struct listnode *postptr, int num)
{
        struct treenode *temp;
        struct listnode *q, *ptr;

        int i,j;
        if(num==0)
                return NULL;

        ptr=postptr;
        for(i=1;i<num;i++)
                ptr = ptr->next;

        /*Now ptr points to last node of postorder which is root*/

        temp=(struct treenode *)malloc(sizeof(struct treenode));
        temp->info=ptr->info;
        temp->lchild = NULL;
        temp->rchild = NULL;

        if(num==1)/*if only one node in tree */
                return temp;

        q=inptr;
        for(i=0; q->info!=ptr->info; i++ )
                q = q->next;

        /*Now i denotes the number of nodes in left subtree
        and q points to root node in inorder list*/

        /*For left subtree*/
        temp->lchild = construct(inptr, postptr, i);

        /*For right subtree*/
        for(j=1;j<=i;j++)
                postptr = postptr->next;
        temp->rchild = construct(q->next, postptr, num-i-1);

        return temp;
}/*End of construct()*/

struct listnode *create_list(struct listnode *start, int n)
{
        int i,data;
        start=NULL;
        for(i=1;i<=n;i++)
        {
                printf("Enter the element to be inserted : ");
                scanf("%d",&data);
                if(start==NULL)
                        start=addtoempty(start,data);
                else
                        start=addatend(start,data);
        }
        return start;
}/*End of create_list()*/

struct listnode *addtoempty(struct listnode *start,int data)
{
        struct listnode *tmp;
        tmp=(struct listnode*)malloc(sizeof(struct listnode));
        tmp->info=data;
        tmp->prev=NULL;
        tmp->next=NULL;
        start=tmp;
        return start;
}/*End of addtoempty( )*/

struct listnode *addatend(struct listnode *start,int data)
{
        struct listnode *tmp,*p;
        tmp=(struct listnode*)malloc(sizeof(struct listnode));
        tmp->info=data;
        p=start;
        while(p->next!=NULL)
                p=p->next;
        p->next=tmp;
        tmp->next=NULL;
        tmp->prev=p;
        return start;
}/*End of addatend( )*/

void inorder(struct treenode *ptr)
{
        if(root==NULL)
        {
                printf("Tree is empty");
                return;
        }
        if(ptr!=NULL)
        {
                inorder(ptr->lchild);
                printf("%d  ",ptr->info);
                inorder(ptr->rchild);
        }
}/*End of inorder( )*/
void postorder(struct treenode *ptr)
{
        if(root==NULL)
        {
                printf("Tree is empty");
                return;
        }
        if(ptr!=NULL)
        {
                postorder(ptr->lchild);
                postorder(ptr->rchild);
                printf("%d  ",ptr->info);
        }
}/*End of postorder( )*/

void preorder(struct treenode *ptr)
{
        if(root==NULL)
        {
                printf("Tree is empty");
                return;
        }
        if(ptr!=NULL)
        {
                printf("%d  ",ptr->info);
                preorder(ptr->lchild);
                preorder(ptr->rchild);
        }
}/*End of preorder( )*/

void display(struct treenode *ptr,int level)
{
        int i;
        if(ptr!=NULL)
        {
                display(ptr->rchild, level+1);
                printf("\n");
                for (i = 0; i < level; i++)
                        printf("    ");
                printf("%d", ptr->info);
                display(ptr->lchild, level+1);
        }
}/*End of display()*/

OUTPUT : :


/* C Program to construct binary tree from inorder and postorder */

Enter the number of nodes  :  7

Enter inorder :
Enter the element to be inserted : 1
Enter the element to be inserted : 2
Enter the element to be inserted : 3
Enter the element to be inserted : 4
Enter the element to be inserted : 5
Enter the element to be inserted : 6
Enter the element to be inserted : 7

Enter postorder:
Enter the element to be inserted : 7
Enter the element to be inserted : 6
Enter the element to be inserted : 5
Enter the element to be inserted : 4
Enter the element to be inserted : 3
Enter the element to be inserted : 2
Enter the element to be inserted : 1

Inorder : 1  2  3  4  5  6  7

Postorder : 7  6  5  4  3  2  1

Preorder : 1  2  3  4  5  6  7


Tree is :

                        7
                    6
                5
            4
        3
    2
1


Process returned 0

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