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#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#if 0
#define PART_1
#else
#define PART_2
#endif
#if 0
#define FILE_PATH "example.txt"
#else
#define FILE_PATH "input.txt"
#endif
int WIDTH = 0;
int HEIGHT = 0;
#define BOARD_SZ ((WIDTH) * (HEIGHT))
char *board;
void parse()
{
FILE *fp = fopen(FILE_PATH, "r");
if(!fp) {
fprintf(stderr, "ERROR: Could not open file: %s", FILE_PATH);
}
char ch;
int i = 0;
// calculate size of the board
while((ch = fgetc(fp)) != EOF)
{
if(ch != '\n') {
i++;
continue;
}
if(WIDTH == 0) WIDTH = i;
}
HEIGHT = i / WIDTH;
board = malloc(BOARD_SZ);
fseek(fp, 0, SEEK_SET);
i = 0;
while((ch = fgetc(fp)) != EOF)
{
if(ch == '\n') continue;
board[i] = ch;
i++;
}
fclose(fp);
}
size_t traverse_map()
{
#ifdef PART_1
int slope_x[1] = {3};
int slope_y[1] = {1};
#define SZ 1
#endif
#ifdef PART_2
int slope_x[5] = {1, 3, 5, 7, 1};
int slope_y[5] = {1, 1, 1, 1, 2};
#define SZ 5
size_t result = 1;
#endif
int x, y;
size_t hit_trees;
for(int i = 0; i < SZ; i++)
{
x = 0;
y = 0;
hit_trees = 0;
while(y != (HEIGHT - 1))
{
x += slope_x[i];
y += slope_y[i];
if(x >= WIDTH)
x = x - WIDTH;
if(board[y * WIDTH + x] == '#')
hit_trees++;
}
#ifdef PART_2
result *= hit_trees;
#endif
}
#ifdef PART_1
return hit_trees;
#endif
#ifdef PART_2
return result;
#endif
}
void print_board()
{
for(int i = 0; i < BOARD_SZ; i++)
{
printf("%c", board[i]);
if(i % WIDTH == (WIDTH - 1))
putc('\n', stdout);
}
}
int main(void)
{
parse();
printf("You hit %ld trees", traverse_map());
free(board);
return 0;
}
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