tree/delete.c

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/**
 * \file
 *
 * \author  Georg Hopp
 *
 * \copyright
 * Copyright © 2012  Georg Hopp
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "tree.h"

Tree inOrderSuccessor(Tree);
void treeRotateLeft(Tree *, Tree);
void treeRotateRight(Tree *, Tree);


void *
treeDelete(Tree * this, const void * search, TreeComp comp)
{
    Tree   node = *this;
    Tree   del_node;

    void * data;

    /*
     * first search for it and if its found return the data
     * and we are done...
     */
    while (NULL != node) {
        int comparison = comp(node->data, search);

        if (0 < comparison) {
            node = TREE_LEFT(node);
            continue;
        }

        if (0 > comparison) {
            node = TREE_RIGHT(node);
            continue;
        }

        if (0 == comparison) {
            break;
        }
    }   

    /*
     * nothing was found...return NULL to indicate this.
     */
    if (NULL == node) {
        return NULL;
    }

    /*
     * we found an element, store its data pointer as we are
     * up to delete it.
     */
    data = node->data;

    /*
     * now remove the element.
     */
    
    /*
     * if we have two children replace data with the one from 
     * out inOrderSuccessor and remove the inOrderSuccessor.
     */
    if (NULL != TREE_LEFT(node) && NULL != TREE_RIGHT(node)) {
        Tree successor = inOrderSuccessor(node);

        node->data = successor->data;
        node       = successor;
    }

    {
        Tree child = TREE_CHILD(node);

        /*
         * if we still have one child replace ourself with it.
         */
        TREE_REPLACE_NODE(this, node, child);

        /*
         * and finally delete the node...and prepare ourselfs
         * for rebalancing.
         */
        if (rbBlack == node->color) {
            if (NULL != child && rbRed == child->color) {
                child->color = rbBlack;
                delete(node);
                return data;
            } else {
                del_node = node;
                if (NULL != child) {
                    node = child;
                } else {
                    node->color = rbBlack;
                    node->left  = NULL;
                    node->right = NULL;
                }
            }
        } else {
            delete(node);
            return data;
        }
    }

    /*
     * now comes rebalancing...note that if we came to this point
     * the node is still not deleted.
     * This is because I am not sure if it is needed during the
     * rebalancing process...(this does not make much sense, but
     * to be honest I don't know now.)
     */
    while(1) {
        // case 1
        if (NULL == TREE_PARENT(node)) {
            break;
        }

        // case 2
        if (NULL != TREE_SIBLING(node)
                && rbRed == TREE_SIBLING(node)->color) {

            TREE_PARENT(node)->color  = rbRed;
            TREE_SIBLING(node)->color = rbBlack;

            if (NULL != TREE_PARENT(node)->right &&
                    node != TREE_PARENT(node)->right) {

                //TREE_ROTATE_LEFT(this, TREE_PARENT(node));
                treeRotateLeft(this, TREE_PARENT(node));

            } else {

                //TREE_ROTATE_RIGHT(this, TREE_PARENT(node));
                treeRotateRight(this, TREE_PARENT(node));

            }
        }

        // case 3 / 4
        if (NULL == TREE_SIBLING(node)
                || (rbBlack == TREE_SIBLING(node)->color
                    && (NULL == TREE_SIBLING(node)->left
                        || rbBlack == TREE_SIBLING(node)->left->color)
                    && (NULL == TREE_SIBLING(node)->right
                        || rbBlack == TREE_SIBLING(node)->right->color))) {

            if (NULL != TREE_SIBLING(node)) {
                TREE_SIBLING(node)->color = rbRed;
            }


            /*
             * this is the point where during the balancing our tree
             * node can be finally deleted.
             */
            if (rbBlack == TREE_PARENT(node)->color) {
                // case 3
                Tree parent = node->parent;
                node = parent;
                continue;
            } else {
                // case 4
                TREE_PARENT(node)->color = rbBlack;
                break;
            }
        }

        // case 5
        if (NULL != TREE_SIBLING(node)
                && rbBlack == TREE_SIBLING(node)->color) {

            if (node == TREE_PARENT(node)->left
                    && (NULL == TREE_SIBLING(node)->right
                        || rbBlack == TREE_SIBLING(node)->right->color)
                    && (NULL != TREE_SIBLING(node)->left
                        && rbRed == TREE_SIBLING(node)->left->color)) {

                TREE_SIBLING(node)->color       = rbRed;
                TREE_SIBLING(node)->left->color = rbBlack;

                //TREE_ROTATE_RIGHT(this, TREE_SIBLING(node));
                treeRotateRight(this, TREE_SIBLING(node));

            } else if (node == TREE_PARENT(node)->right
                    && (NULL == TREE_SIBLING(node)->left
                        || rbBlack == TREE_SIBLING(node)->left->color)
                    && (NULL != TREE_SIBLING(node)->right
                        && rbRed == TREE_SIBLING(node)->right->color)) {

                TREE_SIBLING(node)->color        = rbRed;
                TREE_SIBLING(node)->right->color = rbBlack;

                //TREE_ROTATE_LEFT(this, TREE_SIBLING(node));
                treeRotateLeft(this, TREE_SIBLING(node));
            }
        }
        
        // case 6
        if (NULL != TREE_SIBLING(node)) {
            TREE_SIBLING(node)->color = TREE_PARENT(node)->color;
        }

        if (NULL != node && NULL != TREE_PARENT(node)) {
            TREE_PARENT(node)->color = rbBlack;

            if (NULL != TREE_PARENT(node)->right
                    && node != TREE_PARENT(node)->right) {

                if (NULL != TREE_SIBLING(node)->right) {
                    TREE_SIBLING(node)->right->color = rbBlack;
                }
                //TREE_ROTATE_LEFT(this, TREE_PARENT(node));
                treeRotateLeft(this, TREE_PARENT(node));
            } else {
                if (NULL != TREE_SIBLING(node)->left) {
                    TREE_SIBLING(node)->left->color = rbBlack;
                }
                //TREE_ROTATE_RIGHT(this, TREE_PARENT(node));
                treeRotateRight(this, TREE_PARENT(node));
            }
        }

        break;
    }

    delete(del_node);
    /*
     * not sure if deleting here is correct.
     */
    return data;
}

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