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#include <regex.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define arrlen(x) (sizeof(x)/sizeof((x)[0]))
int
cavepos(int xmin, int xmax, int ymax, int x, int y)
{
if (x < xmin || x > xmax || y < 0 || y > ymax) {
fprintf(stderr, "%s: %d/%d/%d/%d/%d\n", __FUNCTION__, xmin, xmax, ymax, x, y);
return 0;
}
return x - xmin + y * (1 + xmax - xmin);
}
int
cave_resize(char ** cave, int * xmin, int * xmax, int * ymax,
int x, int y)
{
int newxmin, newxmax, newymax;
void * p;
if (y < 0)
// Oops
return -1;
if (y <= *ymax && x >= *xmin && x <= *xmax)
// Nothing to do.
return 0;
newxmin = x < *xmin ? x : *xmin;
newxmax = x > *xmax ? x : *xmax;
newymax = y > *ymax ? y : *ymax;
p = calloc(newymax + 1, 1 + newxmax - newxmin);
if (!p)
return -1;
if (*cave) {
int i;
for (i = 0; i <= *ymax; ++i) {
memcpy(p + i * (1 + newxmax - newxmin) + *xmin - newxmin,
*cave + i * (1 + *xmax - *xmin),
1 + *xmax - *xmin);
}
free(*cave);
}
*cave = p;
*xmin = newxmin;
*xmax = newxmax;
*ymax = newymax;
return 0;
}
#if 0
void
cave_dump(char * cave, int xmin, int xmax, int ymax)
{
int x, y;
for (y = 0; y <= ymax; ++y) {
for (x = xmin; x <= xmax; ++x) {
char c = cave[cavepos(xmin, xmax, ymax, x, y)];
fputc(c ? c : '.', stderr);
}
fputc('\n', stderr);
}
fputc('\n', stderr);
}
#endif
int
main()
{
regex_t coords;
char buf[BUFSIZ];
char * cave = NULL;
int xmin = 500, xmax = 500, ymax = 0;
int grain;
if (regcomp(&coords, "( -> )?([[:digit:]]+),([[:digit:]]+)", REG_EXTENDED) != 0) {
fprintf(stderr, "Bad regex\n");
return -1;
}
// Read the cave
while (fgets(buf, sizeof(buf), stdin)) {
char * pos;
int x, y;
regmatch_t xy[4];
pos = buf;
if (regexec(&coords, pos, arrlen(xy), xy, 0) != 0) {
fprintf(stderr, "No coords found in %s\n", pos);
free(cave);
regfree(&coords);
return -1;
}
x = atoi(buf + xy[2].rm_so);
y = atoi(buf + xy[3].rm_so);
if (cave_resize(&cave, &xmin, &xmax, &ymax, x, y) != 0) {
fprintf(stderr, "Unable to resize cave for %d,%d\n", x, y);
free(cave);
regfree(&coords);
return -1;
}
pos += xy[0].rm_eo;
while (regexec(&coords, pos, arrlen(xy), xy, 0) == 0) {
int newx, newy, i;
newx = atoi(pos + xy[2].rm_so);
newy = atoi(pos + xy[3].rm_so);
if (cave_resize(&cave, &xmin, &xmax, &ymax, newx, newy) != 0) {
fprintf(stderr, "Unable to resize cave for %d,%d\n", newx, newy);
free(cave);
regfree(&coords);
return -1;
}
if ((newx != x && newy != y)
|| (newx == x && newy == y))
{
fprintf(stderr, "Unexpected %d,%d -> %d,%d\n", x, y, newx, newy);
}
else if (newx != x) {
for (i = x; i < newx; ++i) {
cave[cavepos(xmin, xmax, ymax, i, y)] = '#';
}
for (i = x; i > newx; --i) {
cave[cavepos(xmin, xmax, ymax, i, y)] = '#';
}
}
else if (newy != y) {
for (i = y; i < newy; ++i) {
cave[cavepos(xmin, xmax, ymax, x, i)] = '#';
}
for (i = y; i > newy; --i) {
cave[cavepos(xmin, xmax, ymax, x, i)] = '#';
}
}
x = newx;
y = newy;
pos += xy[0].rm_eo;
}
cave[cavepos(xmin, xmax, ymax, x, y)] = '#';
if (*pos != '\n') {
fprintf(stderr, "Unexpected remaining line: %s\n", pos);
}
}
#if 0
cave_dump(cave, xmin, xmax, ymax);
#endif
// Simulate sand
for (grain = 0; 1; ++grain) {
int x, y;
x = 500;
if (cave[cavepos(xmin, xmax, ymax, x, 0)] != '\0')
// Grain can't enter the cave!
break;
// Don't go to "y <= ymax" here. If the grain gets to ymax, it's
// falling off the bottom as there's nothing below it. And an
// attempt to look at the row below isn't valid.
for (y = 0; y < ymax; ++y) {
if (cave[cavepos(xmin, xmax, ymax, x, y + 1)] == '\0') {
// Do nothing, drop down one
(void) 0;
}
else if (x == xmin) {
// Fall off left edge
--x;
break;
}
else if (cave[cavepos(xmin, xmax, ymax, x - 1, y + 1)] == '\0') {
// Drop down and left
--x;
}
else if (x == xmax) {
// Fall off right edge
++x;
break;
}
else if (cave[cavepos(xmin, xmax, ymax, x + 1, y + 1)] == '\0') {
// Drop down and right
++x;
}
else {
// Settle
cave[cavepos(xmin, xmax, ymax, x, y)] = 'o';
break;
}
}
#if 0
cave_dump(cave, xmin, xmax, ymax);
#endif
if (x < xmin || x > xmax || y >= ymax)
// Grain fell out of cave
break;
}
printf("Grains: %d\n", grain);
free(cave);
regfree(&coords);
return 0;
}
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