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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"
#define IDS 4
#else
#define FILE_PATH "input.txt"
#define IDS 908
#endif
#define LOWER(min, max) ((max) - (((max) - (min))/2 + 1))
#define UPPER(min, max) (((min) + (max))/2 + 1)
#define ROWS 128
#define COLUMNS 8
int highest_id = 0;
int ids[IDS] = {0};
void process_pass(char *pass, int index)
{
int min_r = 0; int max_r = ROWS - 1;
int min_c = 0; int max_c = COLUMNS - 1;
for(int i = 0; i < 10; i++)
{
switch(pass[i])
{
case 'F':
max_r = LOWER(min_r, max_r);
break;
case 'B':
min_r = UPPER(min_r, max_r);
break;
case 'L':
max_c = LOWER(min_c, max_c);
break;
case 'R':
min_c = UPPER(min_c, max_c);
break;
}
}
int id = min_r * 8 + min_c;
#ifdef PART_1
(void)index;
if(id > highest_id) highest_id = id;
#endif
#ifdef PART_2
assert(index < IDS);
ids[index] = id;
#endif
}
void parse()
{
FILE *fp = fopen(FILE_PATH, "r");
if(!fp) {
fprintf(stderr, "ERROR: Could not open file: %s\n", FILE_PATH);
exit(EXIT_FAILURE);
}
int i = 0;
char line[256] = {0};
while(fgets(line, sizeof(line), fp) != NULL)
{
if(line[10] == '\n') line[10] = '\0';
process_pass(line, i);
i++;
}
fclose(fp);
}
int find_id()
{
int your_seat;
int seat_missing;
for(int i = 0; i < IDS; i++)
{
your_seat = -1;
seat_missing = 0;
for(int j = 0; j < IDS; j++)
{
if(ids[i] == (ids[j] + 2))
{
your_seat = ids[i] - 1;
seat_missing = 1;
for(int k = 0; k < IDS; k++)
if(your_seat == ids[k]) seat_missing = 0;
}
}
if(your_seat!= -1 && seat_missing != 0)
return your_seat;
}
return -1;
}
void part_1()
{
printf("Highest boarding ID is %d\n", highest_id);
}
void part_2()
{
printf("Your id is: %d\n", find_id());
}
int main(void)
{
parse();
#ifdef PART_1
part_1();
#endif
#ifdef PART_2
part_2();
#endif
return 0;
}
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