avl.c revision 1.4
1 /* $NetBSD: avl.c,v 1.4 2003/06/23 13:05:48 agc 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 <sys/cdefs.h> 50 51 #ifndef lint 52 __RCSID("$NetBSD: avl.c,v 1.4 2003/06/23 13:05:48 agc Exp $"); 53 #endif 54 55 56 #include <string.h> 57 58 #include "defs.h" 59 60 /* find_id returns a pointer to node in TREE that has the correct 61 ID. If there is no node in TREE with ID, NULL is returned. */ 62 63 id_rec * 64 find_id (id_rec *tree, char *id) 65 { 66 int cmp_result; 67 68 /* Check for an empty tree. */ 69 if (tree == NULL) 70 return NULL; 71 72 /* Recursively search the tree. */ 73 cmp_result = strcmp (id, tree->id); 74 if (cmp_result == 0) 75 return tree; /* This is the item. */ 76 else if (cmp_result < 0) 77 return find_id (tree->left, id); 78 else 79 return find_id (tree->right, id); 80 } 81 82 83 /* insert_id inserts a NEW_ID rec into the tree whose ROOT is 84 provided. insert_id returns TRUE if the tree height from 85 ROOT down is increased otherwise it returns FALSE. This is a 86 recursive balanced binary tree insertion algorithm. */ 87 88 int insert_id (id_rec **root, id_rec *new_id) 89 { 90 id_rec *A, *B; 91 92 /* If root is NULL, this where it is to be inserted. */ 93 if (*root == NULL) 94 { 95 *root = new_id; 96 new_id->left = NULL; 97 new_id->right = NULL; 98 new_id->balance = 0; 99 return (TRUE); 100 } 101 102 /* We need to search for a leaf. */ 103 if (strcmp (new_id->id, (*root)->id) < 0) 104 { 105 /* Insert it on the left. */ 106 if (insert_id (&((*root)->left), new_id)) 107 { 108 /* The height increased. */ 109 (*root)->balance --; 110 111 switch ((*root)->balance) 112 { 113 case 0: /* no height increase. */ 114 return (FALSE); 115 case -1: /* height increase. */ 116 return (TRUE); 117 case -2: /* we need to do a rebalancing act. */ 118 A = *root; 119 B = (*root)->left; 120 if (B->balance <= 0) 121 { 122 /* Single Rotate. */ 123 A->left = B->right; 124 B->right = A; 125 *root = B; 126 A->balance = 0; 127 B->balance = 0; 128 } 129 else 130 { 131 /* Double Rotate. */ 132 *root = B->right; 133 B->right = (*root)->left; 134 A->left = (*root)->right; 135 (*root)->left = B; 136 (*root)->right = A; 137 switch ((*root)->balance) 138 { 139 case -1: 140 A->balance = 1; 141 B->balance = 0; 142 break; 143 case 0: 144 A->balance = 0; 145 B->balance = 0; 146 break; 147 case 1: 148 A->balance = 0; 149 B->balance = -1; 150 break; 151 } 152 (*root)->balance = 0; 153 } 154 } 155 } 156 } 157 else 158 { 159 /* Insert it on the right. */ 160 if (insert_id (&((*root)->right), new_id)) 161 { 162 /* The height increased. */ 163 (*root)->balance ++; 164 switch ((*root)->balance) 165 { 166 case 0: /* no height increase. */ 167 return (FALSE); 168 case 1: /* height increase. */ 169 return (TRUE); 170 case 2: /* we need to do a rebalancing act. */ 171 A = *root; 172 B = (*root)->right; 173 if (B->balance >= 0) 174 { 175 /* Single Rotate. */ 176 A->right = B->left; 177 B->left = A; 178 *root = B; 179 A->balance = 0; 180 B->balance = 0; 181 } 182 else 183 { 184 /* Double Rotate. */ 185 *root = B->left; 186 B->left = (*root)->right; 187 A->right = (*root)->left; 188 (*root)->left = A; 189 (*root)->right = B; 190 switch ((*root)->balance) 191 { 192 case -1: 193 A->balance = 0; 194 B->balance = 1; 195 break; 196 case 0: 197 A->balance = 0; 198 B->balance = 0; 199 break; 200 case 1: 201 A->balance = -1; 202 B->balance = 0; 203 break; 204 } 205 (*root)->balance = 0; 206 } 207 } 208 } 209 } 210 211 /* If we fall through to here, the tree did not grow in height. */ 212 return (FALSE); 213 } 214
Indexes created Mon Sep 22 21:09:42 GMT 2025