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//#define _GNU_SOURCE
#include <regex.h>
#include <search.h>
#include <stdio.h>
#include <stdlib.h>
#define arrlen(x) (sizeof(x)/sizeof((x)[0]))
struct point {
int x;
int y;
int z;
};
int
point_cmp(struct point const * a, struct point const * b)
{
if (a->x != b->x)
return a->x - b->x;
if (a->y != b->y)
return a->y - b->y;
return a->z - b->z;
}
int
point_cmp_t(void const * a, void const * b)
{
return point_cmp(a, b);
}
// Get one of the faces of a cube
//
// x = left-right
// y = up-down
// z = front-back
//
// To uniquely identify the faces of a cube, we scale the cube by a factor of
// two, and then identify each face by the point at the face's center.
struct point *
cube_face(int x, int y, int z, int face)
{
struct point * f;
x *= 2;
y *= 2;
z *= 2;
switch (face) {
case 0: // Bottom face
x += 1;
z += 1;
break;
case 1: // Top face
x += 1;
y += 2;
z += 1;
break;
case 2: // Left face
y += 1;
z += 1;
break;
case 3: // Right face
x += 2;
y += 1;
z += 1;
break;
case 4: // Front face
x += 1;
y += 1;
break;
case 5: // Back face
x += 1;
y += 1;
z += 2;
break;
default:
return NULL;
}
if ((f = malloc(sizeof(struct point))) == NULL)
return NULL;
f->x = x;
f->y = y;
f->z = z;
return f;
}
int
main()
{
char buf[BUFSIZ];
regex_t cube;
regmatch_t coords[4];
void * faces = NULL;
int nfaces = 0;
if (regcomp(&cube, "(-?[[:digit:]]+),(-?[[:digit:]]+),(-?[[:digit:]]+)", REG_EXTENDED) != 0) {
fprintf(stderr, "Bad regex\n");
return -1;
}
while (fgets(buf, sizeof(buf), stdin)
&& regexec(&cube, buf, arrlen(coords), coords, 0) == 0)
{
int x, y, z, f;
x = atoi(buf + coords[1].rm_so);
y = atoi(buf + coords[2].rm_so);
z = atoi(buf + coords[3].rm_so);
for (f = 0; f < 6; ++f) {
struct point * face = cube_face(x, y, z, f);
struct point * exists = *((struct point **) tsearch(face, &faces, point_cmp_t));
if (exists == face) {
// Inserted new face
++nfaces;
}
else {
// Face already existed, so delete it
tdelete(face, &faces, point_cmp_t);
--nfaces;
free(face);
free(exists);
}
}
}
printf("Faces: %d\n", nfaces);
#ifdef _GNU_SOURCE
tdestroy(faces, free);
#endif
regfree(&cube);
return 0;
}
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