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#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#define ROPELEN 10
#define UP(head) ((head).y++)
#define DOWN(head) ((head).y--)
#define LEFT(head) ((head).x--)
#define RIGHT(head) ((head).x++)
struct point {
long x, y;
};
struct visited {
size_t len;
struct point *p;
};
void *
emalloc(size_t size) {
void *p = calloc(size, 1);
if (p == NULL) {
perror("emalloc");
exit(1);
}
return p;
}
struct visited *
visited_init(void) {
struct visited *v;
v = emalloc(sizeof (struct visited));
v->p = emalloc(sizeof (struct point));
v->len = 1;
v->p[0].x = v->p[0].y = 0;
return v;
}
void
visited_destroy(struct visited *v) {
if (v) {
free(v->p);
free(v);
}
}
int
check_visited(struct point *p, struct visited *v) {
for (size_t i = 0; i < v->len; i++) {
if ((v->p[i].x == p->x) &&
(v->p[i].y == p->y))
return 1;
}
return 0;
}
void
visit(struct point *tail, struct visited **v) {
if (check_visited(tail, *v) == 1)
return;
struct point *tmp = realloc((*v)->p, sizeof(struct point) * ((*v)->len + 1));
if (tmp == NULL) {
free((*v)->p);
free(*v);
perror("realloc");
exit(1);
}
tmp[(*v)->len].x = tail->x;
tmp[(*v)->len].y = tail->y;
(*v)->p = tmp;
(*v)->len++;
return;
}
void
update_tail(struct point *h, struct point *t) {
long dx = h->x - t->x;
long dy = h->y - t->y;
double d = sqrt((dx * dx) + (dy * dy));
if (d < 2.0)
return;
if (h->x == t->x) {
t->y += h->y > t->y ? 1 : -1;
} else if (h->y == t->y) {
t->x += h->x > t->x ? 1 : -1;
} else {
t->x += h->x > t->x ? 1 : -1;
t->y += h->y > t->y ? 1 : -1;
}
}
int
main(int argc, char **argv) {
char *buf = NULL;
size_t buflen = 0;
ssize_t n;
FILE *f;
struct visited *v1, *v2;
struct point rope[ROPELEN] = {0};
v1 = visited_init();
v2 = visited_init();
if (argc != 2) {
fprintf(stderr, "usage: %s input\n", argv[0]);
return 1;
}
f = fopen(argv[1], "r");
if (f == NULL) {
perror(argv[1]);
return 1;
}
while ((n = getline(&buf, &buflen, f)) != -1) {
if (buf[n - 1] == '\n') {
buf[n - 1] = '\0';
n--;
}
int num;
if (sscanf(buf+2, "%d", &num) != 1) {
perror("sscanf");
return 1;
}
for (int i = 0; i < num; i++) {
switch (buf[0]) {
case 'U':
UP(rope[0]);
break;
case 'D':
DOWN(rope[0]);
break;
case 'L':
LEFT(rope[0]);
break;
case 'R':
RIGHT(rope[0]);
break;
default:
fprintf(stderr, "unknown command \"%s\"\n", buf);
return 1;
}
for (size_t i = 1; i < ROPELEN; i++)
update_tail(&rope[i - 1], &rope[i]);
/* Keep track of the knot immediately after the head (A), and the last knot (B). */
visit(&rope[1], &v1);
visit(&rope[ROPELEN-1], &v2);
}
}
printf( "Part A: %ld\n"
"Part B: %ld\n",
v1->len,
v2->len);
visited_destroy(v1);
visited_destroy(v2);
free(buf);
fclose(f);
return 0;
}
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