1 // ******************************************************************************
2 //
3 // Title: Force Field X.
4 // Description: Force Field X - Software for Molecular Biophysics.
5 // Copyright: Copyright (c) Michael J. Schnieders 2001-2025.
6 //
7 // This file is part of Force Field X.
8 //
9 // Force Field X is free software; you can redistribute it and/or modify it
10 // under the terms of the GNU General Public License version 3 as published by
11 // the Free Software Foundation.
12 //
13 // Force Field X is distributed in the hope that it will be useful, but WITHOUT
14 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
15 // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
16 // details.
17 //
18 // You should have received a copy of the GNU General Public License along with
19 // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
20 // Place, Suite 330, Boston, MA 02111-1307 USA
21 //
22 // Linking this library statically or dynamically with other modules is making a
23 // combined work based on this library. Thus, the terms and conditions of the
24 // GNU General Public License cover the whole combination.
25 //
26 // As a special exception, the copyright holders of this library give you
27 // permission to link this library with independent modules to produce an
28 // executable, regardless of the license terms of these independent modules, and
29 // to copy and distribute the resulting executable under terms of your choice,
30 // provided that you also meet, for each linked independent module, the terms
31 // and conditions of the license of that module. An independent module is a
32 // module which is not derived from or based on this library. If you modify this
33 // library, you may extend this exception to your version of the library, but
34 // you are not obligated to do so. If you do not wish to do so, delete this
35 // exception statement from your version.
36 //
37 // ******************************************************************************
38 package ffx.numerics.quickhull;
39
40 /**
41 * Maintains a single-linked list of faces for use by QuickHull3D.
42 *
43 * @author John E. Lloyd, Fall 2004
44 * @author Michael J. Schnieders
45 * @since 1.0
46 */
47 public class FaceList {
48
49 private Face head;
50
51 private Face tail;
52
53 /**
54 * Clears this list.
55 */
56 public void clear() {
57 head = tail = null;
58 }
59
60 /**
61 * Adds a face to the end of this list.
62 *
63 * @param vtx face to add
64 */
65 public void add(Face vtx) {
66 if (head == null) {
67 head = vtx;
68 } else {
69 tail.next = vtx;
70 }
71 vtx.next = null;
72 tail = vtx;
73 }
74
75 /**
76 * Returns the first face in this list (head), or null if empty.
77 *
78 * @return the first Face, or null if the list is empty
79 */
80 public Face first() {
81 return head;
82 }
83
84 /**
85 * Returns true if this list is empty.
86 *
87 * @return true if there are no faces in the list
88 */
89 public boolean isEmpty() {
90 return head == null;
91 }
92 }