AVL tree delete Item in C

Question

As I try to delete some items from my AVL tree, I'm losing as result some other items. You can see this from the example in the picture.

What is wrong with my code?

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

typedef struct Tree{
    int key;
    struct Tree *left,*right;
    int height;
}tree;

int height(tree *t)
{
    if (t == NULL)
        return 0;
    return t->height;
}

int getBalance(tree *t)
{
    if(t==NULL)
        return 0;
    return height(t->left)-height(t->right);
}

int max(int a, int b)
{
    return (a > b)? a : b;
}

tree* newNode(int key)
{
    tree* node = (tree*)malloc(sizeof(tree));
    node->key   = key;
    node->left   = NULL;
    node->right  = NULL;
    node->height = 1;  // new node is initially added at leaf
    return(node);
}
tree* insert(tree* node, int key)
{
    /* 1.  Perform the normal BST rotation */
    if (node == NULL)
        return(newNode(key));

    if (key < node->key)
        node->left  = insert(node->left, key);
    else
        node->right = insert(node->right, key);

    /* 2. Update height of this ancestor node */
    node->height = max(height(node->left), height(node->right)) + 1;
    return node;
}

void print_preorder(tree * tTree)
{
    if(tTree)
    {
        printf("%d ",tTree->key);
        print_preorder(tTree->left);
        print_preorder(tTree->right);
    }

}

void deleteTree(tree * tTree)
{
    if (tTree)
    {
        deleteTree(tTree->left);
        deleteTree(tTree->right);
        free(tTree);
    }
}

tree* minItem(tree *tTree)  /* delete */
{   
    if(tTree->left)
    {
        tTree = tTree->left;
    }
    else;
    return tTree;
}

tree* del(tree *tTree, int delItem) /* delete( main body) */
{
    if(!(tTree))
        return tTree;
    if(delItem < tTree->key)
        tTree->left = del(tTree->left, delItem);
    else 
        if(delItem > tTree->key)
            tTree->right = del(tTree->right, delItem); 
        else 
            if((tTree->left) && (tTree->right))
            {
                tree *tmp=minItem(tTree->right);
                tTree->key = tmp->key;
                if(tTree->right->left)
                    tTree->right = del(tTree->right,tTree->right->left->key); 
                else tTree->right = del(tTree->right,tTree->right->key);       
            }
            else
                if(tTree->left)
                    tTree = tTree->left;
                else
                    tTree = tTree->right;
                return tTree;
}

tree* rotateLeft(tree* t)
{ 
    tree *y = t->right;
    tree *T2 = y->left;

    // Perform rotation
    y->left = t;
    t->right = T2;


    // Update heights
    t->height = max(height(t->left), height(t->right))+1;
    y->height = max(height(y->left), height(y->right))+1;

    // Return new root
    return y;
} 

tree* rotateRight(tree* t)
{ 
    tree *x = t->left;
    tree *T2 = x->right;

    // Perform rotation
    x->right = t;
    t->left = T2;

    // Update heights
    t->height = max(height(t->left), height(t->right))+1;
    x->height = max(height(x->left), height(x->right))+1;

    // Return new root
    return x;
} 

tree *balanceNode(tree *t)
{
    if (!t) return t;
    int balance = getBalance(t);
    if (balance > 1 && getBalance(t->left) >= 0)   /* rotateReight */
        return rotateRight(t);
    if (balance < -1 && getBalance(t->right) <= 0) /* rotateLeft */
        return rotateLeft(t);
    if (balance > 1 && getBalance(t->left) < 0)    /* rotateLeftReight */
    {
        t->left = rotateLeft(t->left);
        return rotateRight(t);
    }
    if (balance < -1 && getBalance(t->right) > 0)  /* rotateReightLeft */
    {
        t->right = rotateRight(t->right);
        return rotateLeft(t);
    }
    return t;
}


int main()
{
    tree *Tree, *delTree;
    Tree = NULL; delTree = NULL; 
    int i, a[]={7,3,9,10,8,1,4,2,6,5};
    for(i=0;i<10;i++) /* construct tree */
        Tree = insert(Tree,a[i]);
    /* Printing nodes of tree */
    printf("Pre Order Display\n");
    print_preorder(Tree);

    printf("\nBalanced Tree\n");
    Tree=balanceNode(Tree);
    print_preorder(Tree);

    while(1)
    {
        printf("\nEnter an Item that You Want to Delete: ");
        scanf("%d",&i);
        printf("\n");
        delTree = del(Tree,i);
        delTree = balanceNode(delTree);
        /*  Pre-order displays root node, left node and then right node. */
        print_preorder(delTree);
    }

    printf("\n");

    deleteTree(Tree);
    deleteTree(delTree);
    printf("\n");
    return 0;
}

Welcome to Stack Overflow! It sounds like you may need to learn how to use a debugger to step through your code. With a good debugger, you can execute your program line by line and see where it is deviating from what you expect. This is an essential tool if you are going to do any programming. Further reading: [How to debug small programs](http://ericlippert.com/2014/03/05/how-to-debug-small-programs/). — Paul R, Feb 09 '16 at 16:41
You also want to look into what *Minimal* complete verifiable code fragment means... :) — David Hoelzer, Feb 09 '16 at 16:50

score 1 · Accepted Answer · answered Feb 09 '16 at 17:01

1

It would probably be best if you figure it out yourself. The print_preorder function could be useful for debugging your code.

The tricky part of the deletion is this code, so you could trace what's happpening there:

        if((tTree->left) && (tTree->right))
        {
            tree *tmp=minItem(tTree->right);
            tTree->key = tmp->key;
            if(tTree->right->left)
                tTree->right = del(tTree->right,tTree->right->left->key); 
            else tTree->right = del(tTree->right,tTree->right->key);       
        }

answered Feb 09 '16 at 17:01

Ilya

5,377
2
18
33

thx, there is an error "cannot access memory at adress 0x0" but I don't see any misstakes. – Qas Feb 09 '16 at 17:21
sorry) I don't understand it – Qas Feb 09 '16 at 17:50
it gives the error from the begin of my print_preorder – Qas Feb 09 '16 at 18:24

score 1 · Answer 2 · answered Feb 09 '16 at 18:55

This version seems to work:

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

typedef struct Tree{
    int key;
    struct Tree *left,*right;
    int height;
}tree;

int height(tree *t)
{
    if (t == NULL)
        return 0;
    return t->height;
}

int getBalance(tree *t)
{
    if(t==NULL)
        return 0;
    return height(t->left)-height(t->right);
}

int max(int a, int b)
{
    return (a > b)? a : b;
}

tree* newNode(int key)
{
    tree* node = (tree*)malloc(sizeof(tree));
    node->key   = key;
    node->left   = NULL;
    node->right  = NULL;
    node->height = 1;  // new node is initially added at leaf
    return(node);
}
tree* insert(tree* node, int key)
{
    /* 1.  Perform the normal BST rotation */
    if (node == NULL)
        return(newNode(key));

    if (key < node->key)
        node->left  = insert(node->left, key);
    else
        node->right = insert(node->right, key);

    /* 2. Update height of this ancestor node */
    node->height = max(height(node->left), height(node->right)) + 1;
    return node;
}

void print_preorder(tree * tTree)
{
    if(tTree)
    {
        printf("%d ",tTree->key);
        print_preorder(tTree->left);
        print_preorder(tTree->right);
    }

}

void deleteTree(tree * tTree)
{
    if (tTree)
    {
        deleteTree(tTree->left);
        deleteTree(tTree->right);
        free(tTree);
    }
}

tree* del(tree *tTree, int delItem) /* delete( main body) */
{
    if(!(tTree))
        return tTree;
    if(delItem < tTree->key)
        tTree->left = del(tTree->left, delItem);
    else 
        if(delItem > tTree->key)
            tTree->right = del(tTree->right, delItem); 
        else 
        {
            tree *oTree = tTree;
            if((tTree->left) && (tTree->right))
            {
                tree *parent = tTree->right;
                tTree = parent->left;
                if (tTree)
                {
                    while(tTree->left)
                    {
                        parent = tTree;
                        tTree = tTree->left;
                    }
                    parent->left = tTree->right;
                    tTree->right = oTree->right;
                }
                else
                    tTree = parent;
                tTree->left = oTree->left;
            }
            else
                if(tTree->left)
                    tTree = tTree->left;
                else
                    tTree = tTree->right;
            free(oTree);
        }
    return tTree;
}

tree* rotateLeft(tree* t)
{ 
    tree *y = t->right;
    tree *T2 = y->left;

    // Perform rotation
    y->left = t;
    t->right = T2;


    // Update heights
    t->height = max(height(t->left), height(t->right))+1;
    y->height = max(height(y->left), height(y->right))+1;

    // Return new root
    return y;
} 

tree* rotateRight(tree* t)
{ 
    tree *x = t->left;
    tree *T2 = x->right;

    // Perform rotation
    x->right = t;
    t->left = T2;

    // Update heights
    t->height = max(height(t->left), height(t->right))+1;
    x->height = max(height(x->left), height(x->right))+1;

    // Return new root
    return x;
} 

tree *balanceNode(tree *t)
{
    if (!t) return t;
    int balance = getBalance(t);
    if (balance > 1 && getBalance(t->left) >= 0)   /* rotateReight */
        return rotateRight(t);
    if (balance < -1 && getBalance(t->right) <= 0) /* rotateLeft */
        return rotateLeft(t);
    if (balance > 1 && getBalance(t->left) < 0)    /* rotateLeftReight */
    {
        t->left = rotateLeft(t->left);
        return rotateRight(t);
    }
    if (balance < -1 && getBalance(t->right) > 0)  /* rotateReightLeft */
    {
        t->right = rotateRight(t->right);
        return rotateLeft(t);
    }
    return t;
}


int main(void)
{
    tree *Tree;
    Tree = NULL;
    int i, a[]={7,3,9,10,8,1,4,2,6,5};
    for(i=0;i<10;i++) /* construct tree */
        Tree = insert(Tree,a[i]);
    /* Printing nodes of tree */
    printf("Pre Order Display\n");
    print_preorder(Tree);

    printf("\nBalanced Tree\n");
    Tree=balanceNode(Tree);
    print_preorder(Tree);

    while(1)
    {
        printf("\nEnter an Item that You Want to Delete: ");
        scanf("%d",&i);
        printf("\n");
        Tree = del(Tree,i);
        printf("After Delete\n");
        /*  Pre-order displays root node, left node and then right node. */
        print_preorder(Tree);
        Tree = balanceNode(Tree);
        printf("\nAfter Balance\n");
        print_preorder(Tree);
    }

    printf("\n");

    deleteTree(Tree);
    printf("\n");
    return 0;
}

However, I ought to point out that this version doesn't maintain the heights when a node is deleted. I leave that as an exercise for someone else. — Ian Abbott, Feb 09 '16 at 19:17

Qas · Answer 3 · 2016-02-09T18:55:20.997

0

yeah! I've used a new variable "delTree" to delete a node from my tree, but if I use the same "Tree" instead of "delTree" it will be OK, what I needed

do
{
    printf("\nEnter an Item that You Want to Delete: ");
    scanf("%d",&i);
    printf("\n");
    Tree = del(Tree,i);
    Tree = balanceNode(Tree);
    print_preorder(Tree);
    i--;
}while(i);

Thanks to all!

edited Feb 09 '16 at 18:55

answered Feb 09 '16 at 18:46

Qas

332
4
12

1

I believe your issue is stemming from how you find the successor to the item you are deleting. – tijko Feb 09 '16 at 18:58
1

Another issue is that you're not freeing the node you're deleting. – Ilya Feb 09 '16 at 19:31

AVL tree delete Item in C

3 Answers3