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#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int count_trees(int inc_right, int inc_down, const char *filename)
{
FILE *file = fopen(filename, "r");
// Include space for newline and string terminator
char buffer[64] = { 0 };
// Start is always safe
fgets(buffer, 64, file);
// strlen includes the newline
int width = strchr(buffer, '\n') - buffer;
int pos = inc_right;
int hit = 0;
for (int i = 1; fgets(buffer, 64, file); i++) {
if (inc_down != 1 && i % inc_down != 0) {
continue;
}
if (buffer[pos] == '#') {
hit++;
}
pos = (pos + inc_right) % width;
}
fclose(file);
return hit;
}
int main(int argc, char *argv[])
{
char *arg = argv[argc - 1];
long mul = (long)count_trees(1, 1, arg) * count_trees(3, 1, arg) * count_trees(5, 1, arg) * count_trees(7, 1, arg) * count_trees(1, 2, arg);
printf("%li\n", mul);
}
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