1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
/*
* esodata - data structures and other things, of varying utility
* Copyright 2022, Ben Culkin
*
* 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 <https://www.gnu.org/licenses/>.
*/
package bjc.esodata;
/**
* Double-sided tape is essentially two tapes stuck together with a shared
* cursor.
*
* The main way a double-sided tape differs is that it can be flipped, allowing
* access to another set of data.
*
* However, there is only one cursor, and the position of the cursor on one side
* is the inverse of the position on the other side.
*
* When one side is extended, a null will be inserted into the inactive side
* regardless of the auto-extension policy of the tape. The policy will still be
* respected for the active side.
*
* All operations that refer to the tape refer to the currently active side of
* the tape, except for flip.
*
* Flip refers to the entire tape for 'obvious' reasons.
*
* @param <T>
* The element type of the tape.
*
* @author bjculkin
*/
public class DoubleTape<T> implements Tape<T>, DoubleSided {
private boolean frontActive;
/* The front-side of the tape. */
private Tape<T> front;
/* The back-side of the tape. */
private Tape<T> back;
/** Create a new empty double-sided tape that doesn't autoextend. */
public DoubleTape() {
this(false);
}
/**
* Create a new empty double-sided tape that follows the specified
* auto-extension policy.
*
* @param autoExtnd
* Whether or not to auto-extend the tape to the right w/
* nulls.
*/
public DoubleTape(final boolean autoExtnd) {
front = new SingleTape<>(autoExtnd);
back = new SingleTape<>(autoExtnd);
frontActive = true;
}
@Override
public T item() {
return front.item();
}
@Override
public void item(final T itm) {
front.item(itm);
}
@Override
public int size() {
return front.size();
}
@Override
public int position() {
return front.position();
}
@Override
public void insertBefore(final T itm) {
front.insertBefore(itm);
back.insertAfter(null);
}
@Override
public void insertAfter(final T itm) {
front.insertAfter(itm);
back.insertBefore(itm);
}
@Override
public T remove() {
back.remove();
return front.remove();
}
@Override
public void first() {
front.first();
back.last();
}
@Override
public void last() {
front.last();
back.first();
}
@Override
public boolean left() {
return left(1);
}
@Override
public boolean left(final int amt) {
final boolean succ = front.left(amt);
if (succ) back.right(amt);
return succ;
}
@Override
public boolean right() {
return right(1);
}
@Override
public boolean right(final int amt) {
final boolean succ = front.right(amt);
if (succ) back.left(amt);
return succ;
}
@Override
public boolean seekTo(int tgtPos) {
return front.seekTo(tgtPos);
}
@Override
public void flip() {
final Tape<T> tmp = front;
front = back;
back = tmp;
frontActive = !frontActive;
}
@Override
public boolean currentSide() {
return frontActive;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + (back == null ? 0 : back.hashCode());
result = prime * result + (front == null ? 0 : front.hashCode());
return result;
}
@Override
public boolean equals(final Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (!(obj instanceof DoubleTape<?>)) return false;
final DoubleTape<?> other = (DoubleTape<?>) obj;
if (back == null) {
if (other.back != null) return false;
} else if (!back.equals(other.back)) {
return false;
}
if (front == null) {
if (other.front != null) return false;
} else if (!front.equals(other.front)) {
return false;
}
return true;
}
@Override
public String toString() {
return String.format("DoubleTape [front=%s, back=%s]", front, back);
}
}
|
