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
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
|
#define _GNU_SOURCE
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Proper modulo operator
#define modulo(n, m) ((((n) % (m)) + (m)) % (m))
enum direction {
D_NORTH = 3,
D_EAST = 0,
D_SOUTH = 1,
D_WEST = 2,
};
char const *
direction_name(enum direction dir)
{
switch (dir) {
case D_NORTH: return "North";
case D_EAST: return "East";
case D_SOUTH: return "South";
case D_WEST: return "West";
}
return NULL;
}
enum direction
direction_turn(enum direction dir, char turn)
{
#define direction_go(d, t) (1000 * (d) + (t))
switch (direction_go(dir, turn)) {
case direction_go(D_NORTH, 'R'):
case direction_go(D_SOUTH, 'L'):
return D_EAST;
case direction_go(D_NORTH, 'L'):
case direction_go(D_SOUTH, 'R'):
return D_WEST;
case direction_go(D_EAST, 'L'):
case direction_go(D_WEST, 'R'):
return D_NORTH;
case direction_go(D_EAST, 'R'):
case direction_go(D_WEST, 'L'):
return D_SOUTH;
}
fprintf(stderr, "Unexpected direction_turn(%d, %c)\n", dir, turn);
return D_NORTH;
#undef direction_go
}
int
map_move(char * map, int cols, int rows, int pos, enum direction dir, int distance)
{
int skip, wrap, base;
switch (dir) {
case D_NORTH:
skip = -cols;
wrap = cols * rows;
break;
case D_EAST:
skip = 1;
wrap = cols;
break;
case D_SOUTH:
skip = cols;
wrap = cols * rows;
break;
case D_WEST:
skip = -1;
wrap = cols;
break;
default:
fprintf(stderr, "Unexpected direction %d\n", dir);
return -1;
}
base = (pos / wrap) * wrap;
while (distance > 0) {
int newpos = base + modulo(pos + skip, wrap);
while (map[newpos] == ' ' || map[newpos] == '\n')
newpos = base + modulo(newpos + skip, wrap);
switch (map[newpos]) {
case '.':
pos = newpos;
--distance;
break;
case '#':
distance = 0;
break;
default:
fprintf(stderr, "Unexpected map character %c\n", map[newpos]);
return -1;
}
}
return pos;
}
int
main()
{
char * buf = NULL, * beg, * end;
long bufsiz = 0, buflen = 0, maxline = 0, lines = 0;
long pos;
enum direction dir;
char distance[8], c;
int dlen = 0;
// Read map data
// Don't try and figure out lines yet, in case we get a line longer than
// our read buffer, which could make things awkward.
while (1) {
if (bufsiz - buflen < BUFSIZ / 2) {
void * p;
bufsiz += BUFSIZ;
if ((p = realloc(buf, bufsiz)) == NULL) {
fprintf(stderr, "Bad realloc(%ld)\n", bufsiz);
free(buf);
return -1;
}
buf = p;
}
if (!fgets(buf + buflen, bufsiz - buflen, stdin))
// End of file!
break;
if (buflen > 0 && buf[buflen] == '\n' && buf[buflen - 1] == '\n')
// End of map input.
break;
buflen += strlen(buf + buflen);
}
// Work out max lines and longest line.
for (beg = buf, lines = 0; beg < buf + buflen; beg = end + 1, ++lines) {
end = memchr(beg, '\n', buf + buflen - beg);
if (end - beg > maxline)
maxline = end - beg;
}
if (maxline == 0 || lines == 0) {
fprintf(stderr, "Unexpected map size (%ld,%ld)\n", maxline, lines);
free(buf);
return -1;
}
++maxline; // Also count the newline on the end of each line.
// Resize the map data buffer to hold a full grid of data
if ((beg = realloc(buf, lines * maxline)) == NULL) {
fprintf(stderr, "Bad realloc(%ld)\n", bufsiz);
free(buf);
return -1;
}
buf = beg;
memset(buf + buflen, ' ', lines * maxline - buflen);
// Move the map data so that it fits the grid properly
for (end = buf + buflen, pos = lines - 1; pos >= 0; end = beg, --pos) {
beg = memrchr(buf, '\n', (end - buf) - 1);
beg = beg ? beg + 1 : buf;
memmove(buf + pos * maxline, beg, (end - beg));
memset(buf + (pos * maxline) + (end - beg) - 1, ' ', maxline - (end - beg) + 1);
buf[pos * maxline + maxline - 1] = '\n';
}
// Set initial position
pos = 0;
dir = D_EAST;
while (buf[pos] != '.') {
++pos;
}
// Read and follow the movement instructions.
while (pos >= 0 && (c = fgetc(stdin)) != EOF) {
if (isdigit(c)) {
distance[dlen++] = c;
}
else if (c == 'L' || c == 'R') {
distance[dlen] = '\0';
pos = map_move(buf, maxline, lines, pos, dir, atoi(distance));
dir = direction_turn(dir, c);
dlen = 0;
}
else if (c == '\n') {
// Cover last bit of distance, if any
distance[dlen] = '\0';
pos = map_move(buf, maxline, lines, pos, dir, atoi(distance));
break;
}
else {
fprintf(stderr, "Unexpected movement instruction (%c)\n", c);
free(buf);
return -1;
}
}
if (pos < 0) {
free(buf);
return -1;
}
// Done.
printf("Password is %ld (%ld,%ld,%d)\n",
1000 * (1 + pos / maxline) + 4 * (1 + pos % maxline) + dir,
(1 + pos % maxline), (1 + pos / maxline), dir);
// Tidy and exit.
free(buf);
return 0;
}
|
