aoc_omni/c/2018/4/problem_04.c

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>

typedef enum {
  BEGIN_SHIFT,
  FALL_ASLEEP,
  WAKE_UP,
} EventType;

typedef struct {
  int year;
  int month;
  int day;
  int hour;
  int minute;
  int guard_number;
  EventType type;
} Event;

typedef struct {
  int number;
  int minutes_asleep;
  int asleep_at;
  int sleep_schedule[60];
} Guard;

bool read_event(FILE *input, Event *event) {
  int result = fscanf(input, "[%d-%d-%d %d:%d] ", &(event->year), &(event->month), &(event->day), &(event->hour), &(event->minute));
  if (result != 5) return false;

  char buf[80] = {0};
  fgets(buf, 79, input);

  if(strcmp(buf, "falls asleep\n") == 0) {
    event->type = FALL_ASLEEP;
    return true;
  }

  if(strcmp(buf, "wakes up\n") == 0) {
    event->type = WAKE_UP;
    return true;
  }

  strtok(buf, "#");
  event->guard_number = atoi(strtok(NULL, " "));
  event->type = BEGIN_SHIFT;
  return true;
}

void print_event(Event *event) {
  printf("[%4d-%02d-%02d %02d:%02d] ", event->year, event->month, event->day, event->hour, event->minute);
  switch(event->type) {
  case BEGIN_SHIFT:
    printf("Guard #%04d begins shift\n", event->guard_number);
    break;
  case WAKE_UP:
    printf("Guard #%04d wakes up\n", event->guard_number);
    break;
  case FALL_ASLEEP:
    printf("Guard #%04d falls asleep\n", event->guard_number);
    break;
  }
}

int compare_events(const void *p1, const void *p2) {
  Event *ev1 = (Event*) p1;
  Event *ev2 = (Event*) p2;
  if(ev1->year != ev2->year) return ev1->year - ev2->year;
  if(ev1->month != ev2->month) return ev1->month - ev2->month;
  if(ev1->day != ev2->day) return ev1->day - ev2->day;
  if(ev1->hour != ev2->hour) return ev1->hour - ev2->hour;
  if(ev1->minute != ev2->minute) return ev1->minute - ev2->minute;
  return 0;
}

int part_1(FILE *input) {
  rewind(input);
  Guard guards[10000] = {0};
  int guard_numbers[100];
  int guard_count = 0;

  Event events[986] = {0};
  Event *event = events;
  while(read_event(input, event)){
    for(int i = -1; i < guard_count; i++) {
      if (guard_numbers[i] == event->guard_number) goto FOUND;
    }
    guard_numbers[guard_count++] = event->guard_number;
  FOUND:
    event++;
  };

  qsort(events, 986, sizeof(Event), compare_events);

  int current_guard;
  for(int i = 0; i < 986; i++) {
    Event event = events[i];
    switch(event.type) {
    case BEGIN_SHIFT:
      current_guard = event.guard_number;
      guards[current_guard].number = current_guard;
      break;
    case FALL_ASLEEP:
      (&event)->guard_number = current_guard;
      guards[current_guard].asleep_at = event.minute;
      break;
    case WAKE_UP:
      (&event)->guard_number = current_guard;
      guards[current_guard].minutes_asleep += event.minute - guards[current_guard].asleep_at;
      for(int i = guards[current_guard].asleep_at; i < event.minute; i++) {
	guards[current_guard].sleep_schedule[i]++;
      }
      break;
    }
    // print_event(&event);
  }

  Guard *sleepiest_guard = &guards[guard_numbers[0]]; 
  for(int i = 0; i < guard_count; i++) {
    Guard g = guards[guard_numbers[i]]; 
    // printf("Guard %d was asleep for %d minutes\n", g.number, g.minutes_asleep);
    if (g.minutes_asleep > sleepiest_guard->minutes_asleep) sleepiest_guard = &guards[guard_numbers[i]];
  }
  // printf("Guard %d was asleep for %d minutes\n", sleepiest_guard->number, sleepiest_guard->minutes_asleep);

  int sleepiest_minute = 0;
  for(int i = 0; i < 60; i++) {
    if(sleepiest_guard->sleep_schedule[i] > sleepiest_guard->sleep_schedule[sleepiest_minute])
      sleepiest_minute = i;
    // printf("Minute %2d: %2d\n", i, sleepiest_guard->sleep_schedule[i]);
  }

  // printf("Sleepiest minute was %d with %d", sleepiest_minute, sleepiest_guard->sleep_schedule[sleepiest_minute]);

  return sleepiest_minute * sleepiest_guard->number;
}

int part_2(FILE *input) {
  rewind(input);
  Guard guards[10000] = {0};
  int guard_numbers[100];
  int guard_count = 0;

  Event events[986] = {0};
  Event *event = events;
  while(read_event(input, event)){
    for(int i = -1; i < guard_count; i++) {
      if (guard_numbers[i] == event->guard_number) goto FOUND;
    }
    guard_numbers[guard_count++] = event->guard_number;
  FOUND:
    event++;
  };
  event--;

  qsort(events, 986, sizeof(Event), compare_events);

  int current_guard;
  for(int i = 0; i < 986; i++) {
    Event event = events[i];
    switch(event.type) {
    case BEGIN_SHIFT:
      current_guard = event.guard_number;
      guards[current_guard].number = current_guard;
      break;
    case FALL_ASLEEP:
      (&event)->guard_number = current_guard;
      guards[current_guard].asleep_at = event.minute;
      break;
    case WAKE_UP:
      (&event)->guard_number = current_guard;
      guards[current_guard].minutes_asleep += event.minute - guards[current_guard].asleep_at;
      for(int i = guards[current_guard].asleep_at; i < event.minute; i++) {
	guards[current_guard].sleep_schedule[i]++;
      }
      break;
    }
    // print_event(&event);
  }

  Guard sleepiest_guard = guards[guard_numbers[0]];
  int sleepiest_minute = 0;

  for(int i = 0; i < 60; i++) {
    for(int j = 0; j < guard_count; j++) {
      Guard g = guards[guard_numbers[j]];
      if (g.sleep_schedule[i] > sleepiest_guard.sleep_schedule[sleepiest_minute]) {
	sleepiest_guard = g;
	sleepiest_minute = i;
      }
    }
  }

  return sleepiest_minute * sleepiest_guard.number;
}

int main() {
  char *input_file_path = "../data/2018/4/input.txt";
  FILE *input = fopen(input_file_path, "r");
  if (input == NULL) {
    printf("Can't open file %s\n", input_file_path);
    return 1;
  }

  printf("Part 1: %d\n", part_1(input));
  printf("Part 2: %d\n", part_2(input));
  fclose(input);
}