added threaded binary tree

data_structures/binary_trees/Threaded_Binary_Tree.c

@@ -0,0 +1,260 @@
+#include<stdio.h>
+#include<stdlib.h>
+
+/*Threaded Binary Tree is a binary tree variant in which all left child
+pointers that are NULL (in Linked list representation) point to its
+in-order predecessor, and all right child pointers that are NULL
+(in Linked list representation) point to its in-order successor.
+
+This file is a simple implementation of a Threaded Binary Tree
+with the following functionalities:
+ - Insertion
+ - Search
+ - Deletion
+ - Listing of node keys inorder,preorder, postorder
+*/
+
+// Node, the basic data structure in the tree
+typedef struct Node
+{
+	int data;
+	struct Node *llink;
+	struct Node *rlink;
+}node;
+
+node* create_node(int data)
+{
+	node *ptr=(node*) malloc(sizeof(node));
+	ptr->rlink=ptr->llink=NULL;
+	ptr->data=data;
+	return ptr;
+}
+
+void insert_BT(node **root,int data)
+{
+	node *new_node=create_node(data);
+	node *temp;  //to be deleted
+	node *prev;  //keeps track of the parent of the element deleted
+	if(*root==NULL)
+	{
+		*root=new_node;
+	}
+	else
+	{
+		temp=*root;
+		prev=NULL;
+		while(temp!=NULL)
+		{
+			if(new_node->data>temp->data)
+			{
+				prev=temp;
+				temp=temp->rlink;
+			}
+			else if(new_node->data<temp->data)
+			{
+				prev=temp;
+				temp=temp->llink;
+			}
+			else
+			{
+				return;
+			}
+		}
+
+		if(new_node->data>prev->data)
+		{
+			prev->rlink=new_node;
+		}
+		else
+		{
+			prev->llink=new_node;
+		}
+	}
+}
+
+// returns "Element found" if the search element is present else returns, "Element not found"
+void search(node *root, int ele)
+{
+	node *temp=root;
+	while(temp!=NULL)
+	{
+		if(temp->data==ele)
+		{
+			break;
+		}
+		else if(ele>temp->data)
+		{
+			temp=temp->rlink;
+		}
+		else
+		{
+			temp=temp->llink;
+		}
+	}
+
+	if(temp==NULL)
+	{
+		printf("%s\n","Element not found." );
+	}
+	else 	printf("%s\n","Element found." );
+}
+
+void inorder_display(node *curr)
+{
+	if(curr!=NULL)
+	{
+		inorder_display(curr->llink);
+		printf("%d\t",curr->data );
+		inorder_display(curr->rlink);
+	}
+
+}
+
+void postorder_BT(node *curr)
+{
+	if(curr!=NULL)
+	{
+		postorder_BT(curr->llink);
+		postorder_BT(curr->rlink);
+		printf("%d\t",curr->data);
+	}
+
+}
+
+void preorder_BT(node *curr)
+{
+	if(curr!=NULL)
+	{
+		printf("%d\t",curr->data);
+		preorder_BT(curr->llink);
+		preorder_BT(curr->rlink);
+	}
+}
+
+// deletes the node if present, else it takes no action.
+void delete_BT(node **root,int ele)
+{
+	node* temp;
+	node *prev;
+	if(*root==NULL)	return;
+	else
+	{
+		temp=*root;
+		prev=NULL;
+		// search
+		while(temp!=NULL)
+		{
+			if(temp->data==ele)
+			{
+				break;
+			}
+			else if(ele>temp->data)
+			{
+				prev=temp;
+				temp=temp->rlink;
+			}
+			else
+			{
+				prev=temp;
+				temp=temp->llink;
+			}
+			}
+		}
+
+		if(temp==NULL)
+			return;
+		else
+		{
+			node *replacement;   //deleted node's replacement
+			node *t;
+			if(temp->llink==NULL && temp->rlink==NULL)
+			{
+				replacement=NULL;
+			}
+			else if(temp->llink==NULL && temp->rlink!=NULL)
+			{
+				replacement=temp->rlink;
+			}
+			else if(temp->llink!=NULL && temp->rlink==NULL)
+			{
+				replacement=temp->llink;
+			}
+			else
+			{
+				replacement=temp->rlink;  //replaced with inorder successor
+				t=replacement;
+				while(t->llink!=NULL)
+				{
+					t=t->llink;
+				}
+				t->llink=temp->llink;  //leftmost node of the replacement is linked to the left child of the deleted node
+			}
+
+			if(temp==*root)
+			{
+				free(*root);
+				*root=replacement;
+			}
+			else if(prev->llink==temp)
+			{
+				free(prev->llink);
+				prev->llink=replacement;
+			}
+			else if(prev->rlink==temp)
+			{
+				free(prev->rlink);
+				prev->rlink=replacement;
+			}
+		}
+	}
+
+
+void main()
+{
+	printf("BINARY TREE: \n");
+	node *root=NULL;
+	int choice,n;
+	do
+	{
+		printf("%s\n","1. Insert into BT" );
+		printf("%s\n","2. Print BT - inorder" );
+		printf("%s\n","3. Print BT - preorder" );
+		printf("%s\n","4. print BT - postorder" );
+		printf("%s\n","5. delete from BT" );
+		printf("%s\n","6. search in BT" );
+		scanf("%d",&choice);
+
+
+	switch(choice)
+	{
+		case 1:
+		printf("%s\n","Enter a no:" );
+		scanf("%d",&n);
+		insert_BT(&root,n);
+		break;
+		case 2:
+		inorder_display(root);
+		printf("\n");
+		break;
+		case 3:
+		preorder_BT(root);
+		printf("\n");
+		break;
+		case 4:
+		postorder_BT(root);
+		printf("\n");
+		break;
+		case 5:
+		printf("%s\n","Enter a no:" );
+		scanf("%d",&n);
+		delete_BT(&root,n);
+		break;
+		case 6:
+		printf("%s\n","Enter a no:" );
+		scanf("%d",&n);
+		search(root,n);
+		break;
+	}
+
+	}while(choice!=0);
+}