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#include <limits.h>
#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define arrlen(x) (sizeof(x)/sizeof((x)[0]))
#define min(x, y) ((x) < (y) ? (x) : (y))
#define max(x, y) ((x) > (y) ? (x) : (y))
struct sensor {
long x;
long y;
long beaconx;
long beacony;
};
long
sensor_distance(struct sensor const * s, long x, long y)
{
return labs(s->x - x) + labs(s->y - y);
}
long
sensor_zone(struct sensor const * s)
{
return sensor_distance(s, s->beaconx, s->beacony);
}
int
sensor_isbeacon(struct sensor const * s, long x, long y)
{
return x == s->beaconx && y == s->beacony;
}
int
main(int argc, char ** argv)
{
regex_t coords;
char buf[BUFSIZ];
struct sensor * sensors = NULL, * s;
int nsensors = 0, i;
long xmin, xmax, ymin, ymax, zone;
long x, y = LONG_MIN, empty = 0;
while ((i = getopt(argc, argv, "y:")) != -1) {
switch (i) {
case 'y':
y = atol(optarg);
break;
default:
return -1;
}
}
if (y == LONG_MIN) {
fprintf(stderr, "Required option: y\n");
return -1;
}
if (regcomp(&coords, "Sensor at x=(-?[[:digit:]]+), y=(-?[[:digit:]]+):"
" closest beacon is at x=(-?[[:digit:]]+), y=(-?[[:digit:]]+)",
REG_EXTENDED) != 0)
{
fprintf(stderr, "Bad regex\n");
return -1;
}
// Read the sensors and their beacons
while (fgets(buf, sizeof(buf), stdin)) {
regmatch_t xy[5];
void * p;
if (regexec(&coords, buf, arrlen(xy), xy, 0) != 0) {
fprintf(stderr, "No coords found in %s\n", buf);
free(sensors);
regfree(&coords);
return -1;
}
if ((p = realloc(sensors, ++nsensors * sizeof(struct sensor))) == NULL) {
fprintf(stderr, "Bad realloc(%zd)\n", nsensors * sizeof(struct sensor));
free(sensors);
regfree(&coords);
return -1;
}
sensors = p;
sensors[nsensors - 1].x = atol(buf + xy[1].rm_so);
sensors[nsensors - 1].y = atol(buf + xy[2].rm_so);
sensors[nsensors - 1].beaconx = atol(buf + xy[3].rm_so);
sensors[nsensors - 1].beacony = atol(buf + xy[4].rm_so);
}
// Calculate max bounds for sensors/beacons
s = sensors;
zone = sensor_zone(s);
xmin = s->x - zone;
xmax = s->x + zone;
ymin = s->y - zone;
ymax = s->y + zone;
for (s = sensors + 1; s < sensors + nsensors; ++s) {
zone = sensor_zone(s);
xmin = min(xmin, s->x - zone);
xmax = max(xmax, s->x + zone);
ymin = min(ymin, s->y - zone);
ymax = max(ymax, s->y + zone);
}
// Check for spots without beacons
for (x = xmin; x <= xmax; ++x) {
for (s = sensors; s < sensors + nsensors; ++s) {
if (sensor_distance(s, x, y) <= sensor_zone(s)
&& !sensor_isbeacon(s, x, y))
{
break;
}
}
if (s < sensors + nsensors)
++empty;
}
printf("Positions without a beacon on row %ld: %ld\n", y, empty);
free(sensors);
regfree(&coords);
return 0;
}
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