Deletion in a Binary Search Tree

This program illustrates deletion in a Binary search Tree.

#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)

{

    int direction;

    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;

    }

}

struct BSTNode*treeMinimum(struct BSTNode*node)

{

   while(node->left!=NULL)

        node=node->left;

   return node;

}

void transplant(struct BST*T,struct BSTNode*u,struct BSTNode*v)

{

    // replacing node u by node v

    if(u->parent==NULL)

        T->root=v;

    else if(u->parent->left!=NULL && u->parent->left->key == u->key)

        u->parent->left=v;

    else if(u->parent->right!=NULL && u->parent->right->key == u->key)

        u->parent->right=v;

    //updating the parent of v

    if(v!=NULL)

        v->parent=u->parent;

}

void BSTDelete(struct BST*T,struct BSTNode*z)

{

    struct BSTNode*y;

    if(z->right == NULL)

        transplant(T,z,z->left);

    else if(z->left == NULL)

        transplant(T,z,z->right);

    else

    {

        y=treeMinimum(z->right);

        if(y->parent!=z)

        {

            transplant(T,y,y->right);

            y->right=z->right;

            y->right->parent=y;

        }

        transplant(T,z,y);

        y->left=z->left;

        y->left->parent=y;

    }

    free(z);

}

int main()

{

    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]);

    BSTDelete(T,nodeArray[3]);

    BSTDelete(T,nodeArray[8]);

    inorderTraversal(T->root);

    return 0;

}

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