Day10 C
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dobiadi
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day10/c/day10
Executable file
BIN
day10/c/day10
Executable file
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269
day10/c/day10.c
Normal file
269
day10/c/day10.c
Normal file
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#define MAX_MAP_SIZE 256
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typedef enum tile_type {
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GROUND,
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UP_DOWN,
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LEFT_RIGHT,
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UP_RIGHT,
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UP_LEFT,
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DOWN_LEFT,
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DOWN_RIGHT,
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START
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} tile_type_t;
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typedef struct tile {
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tile_type_t type;
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struct tile *links[2];
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int part_of_loop;
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} tile_t;
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int main() {
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char *p, *buf, c;
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buf = (char *)malloc(MAX_MAP_SIZE);
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memset(buf, 0, MAX_MAP_SIZE);
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p = buf;
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tile_t map[MAX_MAP_SIZE][MAX_MAP_SIZE];
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memset(map, 0, MAX_MAP_SIZE*MAX_MAP_SIZE*sizeof(tile_t));
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int x = 0, y = 0;
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while ((c = getchar()) != EOF) {
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*p++ = c;
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if (c == '\n') {
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x = 0;
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p = buf;
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while (*p != '\n') {
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switch (*p) {
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case '.':
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map[x][y].type = GROUND;
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break;
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case '|':
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map[x][y].type = UP_DOWN;
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// UP
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if (y != 0) {
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map[x][y].links[0] = &map[x][y-1];
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}
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// DOWN
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map[x][y].links[1] = &map[x][y+1];
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break;
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case '-':
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map[x][y].type = LEFT_RIGHT;
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// LEFT
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if (x != 0) {
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map[x][y].links[0] = &map[x-1][y];
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}
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// RIGHT
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map[x][y].links[1] = &map[x+1][y];
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break;
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case 'L':
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map[x][y].type = UP_RIGHT;
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// UP
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if (y != 0) {
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map[x][y].links[0] = &map[x][y-1];
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}
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// RIGHT
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map[x][y].links[1] = &map[x+1][y];
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break;
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case 'J':
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map[x][y].type = UP_LEFT;
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// UP
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if (y != 0) {
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map[x][y].links[0] = &map[x][y-1];
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}
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// LEFT
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if (x != 0) {
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map[x][y].links[1] = &map[x-1][y];
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}
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break;
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case '7':
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map[x][y].type = DOWN_LEFT;
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// DOWN
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map[x][y].links[0] = &map[x][y+1];
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// LEFT
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if (x != 0) {
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map[x][y].links[1] = &map[x-1][y];
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}
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break;
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case 'F':
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map[x][y].type = DOWN_RIGHT;
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// DOWN
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map[x][y].links[0] = &map[x][y+1];
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// RIGHT
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map[x][y].links[1] = &map[x+1][y];
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break;
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case 'S':
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map[x][y].type = START;
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break;
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}
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p++;
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x++;
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}
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y++;
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memset(buf, 0, MAX_MAP_SIZE);
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p = buf;
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}
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}
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// Find start
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tile_t *start, *curr, *prev;
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int found = 0;
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for (int i = 0; i < y; i++) {
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for (int j = 0; j < x; j++) {
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if (map[j][i].type == START) {
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start = &map[j][i];
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curr = start;
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found = 1;
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int link_num = 0;
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// Connect up start tile
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// UP
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if (i != 0) {
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for (int k = 0; k < 2; k++) {
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if (map[j][i-1].links[k] == start) {
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start->links[link_num] = &map[j][i-1];
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link_num++;
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break;
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}
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}
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}
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// DOWN
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for (int k = 0; k < 2; k++) {
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if (map[j][i+1].links[k] == start) {
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start->links[link_num] = &map[j][i+1];
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link_num++;
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break;
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}
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}
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// LEFT
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if (j != 0) {
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for (int k = 0; k < 2; k++) {
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if (map[j-1][i].links[k] == start) {
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start->links[link_num] = &map[j-1][i];
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link_num++;
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break;
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}
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}
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}
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// RIGHT
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for (int k = 0; k < 2; k++) {
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if (map[j+1][i].links[k] == start) {
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start->links[link_num] = &map[j+1][i];
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link_num++;
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break;
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}
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}
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// Assign the correct type to the start tile, needed for part2
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if (start->links[0] == &map[j][i-1] && start->links[1] == &map[j][i+1]) {
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start->type = UP_DOWN;
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}
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if (start->links[0] == &map[j][i-1] && start->links[1] == &map[j+1][i]) {
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start->type = UP_RIGHT;
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}
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if (start->links[0] == &map[j][i-1] && start->links[1] == &map[j-1][i]) {
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start->type = UP_LEFT;
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}
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if (start->links[0] == &map[j-1][i] && start->links[1] == &map[j+1][i]) {
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start->type = LEFT_RIGHT;
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}
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if (start->links[0] == &map[j][i+1] && start->links[1] == &map[j-1][i]) {
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start->type = DOWN_LEFT;
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}
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if (start->links[0] == &map[j][i+1] && start->links[1] == &map[j+1][i]) {
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start->type = DOWN_RIGHT;
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}
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break;
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}
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}
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if (found) {
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break;
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}
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}
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// Count to loop length
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unsigned long loop_length = 0;
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curr = start->links[0];
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prev = start;
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start->part_of_loop = 1;
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while (curr != start) {
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curr->part_of_loop = 1;
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loop_length++;
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for (int i = 0; i < 2; i++) {
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if (prev != curr->links[i]) {
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prev = curr;
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curr = curr->links[i];
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break;
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}
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}
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}
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unsigned long max_distance = loop_length % 2 ? loop_length / 2 + 1 : loop_length / 2;
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printf("%lu\n", max_distance);
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unsigned long inside_tile_count = 0;
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for (int i = 0; i < y; i++) {
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for (int j = 0; j < x; j++) {
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if (map[j][i].part_of_loop) {
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continue;
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}
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// Start going in a specific direction. (in this case right)
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// If we are inside the pipes we will cross the pipe an odd number of times
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int crosses = 0;
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// If we entered a pipe through F or L we have to keep track whether we cross the pipe when leaving
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int entry = 0;
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for (int k = 1; k < x - j; k++) {
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// We only care about pipes that are part of the loop
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if (!map[j+k][i].part_of_loop) {
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continue;
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}
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// If we are 'inside a pipe' we are no crossing it
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tile_type_t tile_type = map[j+k][i].type;
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if (tile_type == LEFT_RIGHT) {
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continue;
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}
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// Entering the loop. We are not crossing it yet, it depends on the exit tile
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if (tile_type == DOWN_RIGHT || tile_type == UP_RIGHT) {
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if (tile_type == DOWN_RIGHT) {
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entry = 1;
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} else {
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entry = 2;
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}
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continue;
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}
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// Vertical pipe, we are crossing the loop
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if (tile_type == UP_DOWN) {
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crosses += 1;
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entry = 0;
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continue;
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}
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// Exiting loop, check whether we crossed
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if (tile_type == DOWN_LEFT || tile_type == UP_LEFT) {
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if ((tile_type == DOWN_LEFT && entry == 2) || (tile_type == UP_LEFT && entry == 1)) {
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crosses += 1;
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}
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entry = 0;
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continue;
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}
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}
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if (crosses % 2) {
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inside_tile_count++;
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}
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}
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}
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printf("%lu\n", inside_tile_count);
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free(buf);
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}
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