1 /* $NetBSD: avl.c,v 1.3 2002/03/21 05:15:39 phil Exp $ */ 2 3 /* 4 * Copyright (c) 1997 Philip A. Nelson. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. All advertising materials mentioning features or use of this software 16 * must display the following acknowledgement: 17 * This product includes software developed by Philip A. Nelson. 18 * 4. The name of Philip A. Nelson may not be used to endorse or promote 19 * products derived from this software without specific prior written 20 * permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY PHILIP NELSON ``AS IS'' AND ANY EXPRESS OR 23 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 24 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 25 * IN NO EVENT SHALL PHILIP NELSON BE LIABLE FOR ANY DIRECT, INDIRECT, 26 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 27 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 31 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32 */ 33 34 /* avl.c: Routines for manipulation an avl tree. 35 * 36 * an include file should define the following minimum struct.: 37 * (Comments must be made into real comments.) 38 * 39 * typedef struct id_rec { 40 * / * The balanced binary tree fields. * / 41 * char *id; / * The name. * / 42 * short balance; / * For the balanced tree. * / 43 * struct id_rec *left, *right; / * Tree pointers. * / 44 * 45 * / * Other information fields. * / 46 * } id_rec; 47 */ 48 49 #include <string.h> 50 51 #include "defs.h" 52 53 /* find_id returns a pointer to node in TREE that has the correct 54 ID. If there is no node in TREE with ID, NULL is returned. */ 55 56 id_rec * 57 find_id (id_rec *tree, char *id) 58 { 59 int cmp_result; 60 61 /* Check for an empty tree. */ 62 if (tree == NULL) 63 return NULL; 64 65 /* Recursively search the tree. */ 66 cmp_result = strcmp (id, tree->id); 67 if (cmp_result == 0) 68 return tree; /* This is the item. */ 69 else if (cmp_result < 0) 70 return find_id (tree->left, id); 71 else 72 return find_id (tree->right, id); 73 } 74 75 76 /* insert_id inserts a NEW_ID rec into the tree whose ROOT is 77 provided. insert_id returns TRUE if the tree height from 78 ROOT down is increased otherwise it returns FALSE. This is a 79 recursive balanced binary tree insertion algorithm. */ 80 81 int insert_id (id_rec **root, id_rec *new_id) 82 { 83 id_rec *A, *B; 84 85 /* If root is NULL, this where it is to be inserted. */ 86 if (*root == NULL) 87 { 88 *root = new_id; 89 new_id->left = NULL; 90 new_id->right = NULL; 91 new_id->balance = 0; 92 return (TRUE); 93 } 94 95 /* We need to search for a leaf. */ 96 if (strcmp (new_id->id, (*root)->id) < 0) 97 { 98 /* Insert it on the left. */ 99 if (insert_id (&((*root)->left), new_id)) 100 { 101 /* The height increased. */ 102 (*root)->balance --; 103 104 switch ((*root)->balance) 105 { 106 case 0: /* no height increase. */ 107 return (FALSE); 108 case -1: /* height increase. */ 109 return (TRUE); 110 case -2: /* we need to do a rebalancing act. */ 111 A = *root; 112 B = (*root)->left; 113 if (B->balance <= 0) 114 { 115 /* Single Rotate. */ 116 A->left = B->right; 117 B->right = A; 118 *root = B; 119 A->balance = 0; 120 B->balance = 0; 121 } 122 else 123 { 124 /* Double Rotate. */ 125 *root = B->right; 126 B->right = (*root)->left; 127 A->left = (*root)->right; 128 (*root)->left = B; 129 (*root)->right = A; 130 switch ((*root)->balance) 131 { 132 case -1: 133 A->balance = 1; 134 B->balance = 0; 135 break; 136 case 0: 137 A->balance = 0; 138 B->balance = 0; 139 break; 140 case 1: 141 A->balance = 0; 142 B->balance = -1; 143 break; 144 } 145 (*root)->balance = 0; 146 } 147 } 148 } 149 } 150 else 151 { 152 /* Insert it on the right. */ 153 if (insert_id (&((*root)->right), new_id)) 154 { 155 /* The height increased. */ 156 (*root)->balance ++; 157 switch ((*root)->balance) 158 { 159 case 0: /* no height increase. */ 160 return (FALSE); 161 case 1: /* height increase. */ 162 return (TRUE); 163 case 2: /* we need to do a rebalancing act. */ 164 A = *root; 165 B = (*root)->right; 166 if (B->balance >= 0) 167 { 168 /* Single Rotate. */ 169 A->right = B->left; 170 B->left = A; 171 *root = B; 172 A->balance = 0; 173 B->balance = 0; 174 } 175 else 176 { 177 /* Double Rotate. */ 178 *root = B->left; 179 B->left = (*root)->right; 180 A->right = (*root)->left; 181 (*root)->left = A; 182 (*root)->right = B; 183 switch ((*root)->balance) 184 { 185 case -1: 186 A->balance = 0; 187 B->balance = 1; 188 break; 189 case 0: 190 A->balance = 0; 191 B->balance = 0; 192 break; 193 case 1: 194 A->balance = -1; 195 B->balance = 0; 196 break; 197 } 198 (*root)->balance = 0; 199 } 200 } 201 } 202 } 203 204 /* If we fall through to here, the tree did not grow in height. */ 205 return (FALSE); 206 } 207