Searching in a Binary Search Tree - Recursive and Iterative Search

The following program illustrates the Insertion along with searching in a Binary Search Tree.

Searching in a Binary Search Tree can be performed by the following two ways:

1. 1.  Recursive search
2. 2.  Iterative search

#include<stdio.h>

#include<stdlib.h>

struct BSTNode

{

      /*

       * this is the basic structure representing a node of the Tree

       */

    int key; // key stores the data part of the node.

    struct BSTNode *left,*right,*parent;

    /*

     * the left pointer points to the left child

     * right pointer points to the right child

     * parent points to the parent of this node.

     */

};

struct BST

{

      /*

       * Any binary search tree can be identified alone by its root.

       */

    struct BSTNode *root;

};

struct BSTNode*makeNode(int key)

{

    struct BSTNode*newNode;

    newNode=(struct BSTNode*)malloc(sizeof(struct BSTNode));

    newNode->key=key;

    newNode->left=newNode->right=newNode->parent=NULL;

    return newNode;

}

void inorderTraversal(struct BSTNode*root)

{

    if(root==NULL)

        return;

    inorderTraversal(root->left);

    printf("%d ",root->key);

    inorderTraversal(root->right);

}

void BSTInsert(struct BST*T,struct BSTNode*newNode)

{

    struct BSTNode*currentNode,*previousNode;

    if(T->root==NULL)

        T->root=newNode;

    else

    {

        currentNode=T->root;

        while(currentNode!=NULL)

        {

            previousNode=currentNode;

            if(currentNode->key > newNode->key)

                currentNode=currentNode->left;

            else

                currentNode=currentNode->right;

        }

        if(newNode->key < previousNode->key)

            previousNode->left=newNode;

        else

            previousNode->right=newNode;

        newNode->parent=previousNode;

    }

}

/*

    the following search functions searches and returns node with key value k

    if no such node is found it returns null.

    Note that the search functionality is implemented in the sub tree rooted at x.

*/

struct BSTNode*iterativeBSTSearch(struct BSTNode*x,int k)

{

    while(x!=NULL && x->key!=k)

        if(x->key < k)

            x=x->right;

        else

            x=x->left;

    return x;

}

struct BSTNode*recursiveBSTSearch(struct BSTNode*x,int k)

{

    if(x==NULL || k==x->key)

        return x;

    else if(x->key < k)

        return recursiveBSTSearch(x->right,k);

    else

        return recursiveBSTSearch(x->left,k);

}

int main()

{

    struct BSTNode*x;

    struct BST*T;

    T=(struct BST*)malloc(sizeof(struct BST*));

    T->root=NULL;

    struct BSTNode **nodeArray;

    nodeArray=(struct BSTNode**)malloc(sizeof(struct BstNode*)*10);

    nodeArray[0]=makeNode(500);

    nodeArray[1]=makeNode(200);

    nodeArray[2]=makeNode(700);

    nodeArray[3]=makeNode(100);

    nodeArray[4]=makeNode(300);

    nodeArray[5]=makeNode(400);

    nodeArray[6]=makeNode(600);

    nodeArray[7]=makeNode(0);

    nodeArray[8]=makeNode(900);

    nodeArray[9]=makeNode(800);

    BSTInsert(T,nodeArray[0]);

    BSTInsert(T,nodeArray[1]);

    BSTInsert(T,nodeArray[2]);

    BSTInsert(T,nodeArray[3]);

    BSTInsert(T,nodeArray[4]);

    BSTInsert(T,nodeArray[5]);

    BSTInsert(T,nodeArray[6]);

    BSTInsert(T,nodeArray[7]);

    BSTInsert(T,nodeArray[8]);

    BSTInsert(T,nodeArray[9]);

    x=recursiveBSTSearch(nodeArray[0],600);

    if(x==NULL)

        printf("No Node found with given key value\n");

    else

        printf("Node found with given key value\n");

    x=iterativeBSTSearch(nodeArray[0],600);

    if(x==NULL)

        printf("No Node found with given key value\n");

    else

        printf("Node found with given key value\n");

    x=recursiveBSTSearch(nodeArray[0],650);

    if(x==NULL)

        printf("No Node found with given key value\n");

    else

        printf("Node found with given key value\n");

    x=iterativeBSTSearch(nodeArray[0],650);

    if(x==NULL)

        printf("No Node found with given key value\n");

    else

        printf("Node found with given key value\n");

    return 0;

}

For complete program of Binary search Tree in C visit here and here (for program as per guidelines provided by Cormen)