advent-of-code/2022/3.c

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

// Find badges for part 2
char find_badge(char group[3][50]) {

  for (int i = 0; i < strlen(group[0]); i++) {
    for (int j = 0; j < strlen(group[1]); j++) {
      for (int k = 0; k < strlen(group[2]); k++) {
        if (group[0][i] == group[1][j] && group[1][j] == group[2][k]) {
          return group[0][i];
        }
      }
    }
  }
  return 0;
}

// Find items for part 1
char find_item(char *items) {

  int len = strlen(items);
  int mid = len / 2;

  for (int i = 0; i < mid; i++) {
    for (int j = mid; j < len; j++) {
      if (items[i] == items[j]) {
        return items[i];
      }
    }
  }
  return 0;
}

// Updates item_sum / badge_sum when match is found
void update_sum(const char c, int *sum) {

  if (c > 64 && c < 91) {
    *sum += c - 38;
  } else if (c > 96 && c < 123) {
    *sum += c - 96;
  }
}

int main(int argc, char *argv[]) {

  if (argc != 2) {
    fprintf(stderr, "USAGE: %s input_file\n", argv[0]);
    return 1;
  }

  FILE *file = fopen(argv[1], "r");
  if (!file) {
    perror("fopen");
    return 1;
  }

  char items[50] = {0};
  char group[3][50] = {0};
  int item_sum = 0, badge_sum = 0, idx = 0;

  while (fgets(items, sizeof items / sizeof *items, file) != NULL) {

    if (strlen(items) == 1) {
      break;
    }

    // Part 1 - find misplaced items
    items[strlen(items) - 1] = '\0';
    char match = find_item(items);
    if (!match) {
      fprintf(stderr, "Match not found: %s\n", items);
    }

    update_sum(match, &item_sum);

    // Part 2 - find badges among groups of 3
    memcpy(group[idx], items, strlen(items));
    idx++;

    if (idx == 3) {
      idx = 0;
      char badge = find_badge(group);
      if (!badge) {
        fprintf(stderr,
                "Badge not found among the following group:\n%s\n%s\n%s\n",
                group[0], group[1], group[2]);
      }

      update_sum(badge, &badge_sum);

      for (int i = 0; i < sizeof group / sizeof *group; i++) {
        memset(group[i], 0, sizeof group[0] / sizeof *group[0]);
      }
    }
    memset(items, 0, sizeof items / sizeof *items);
  }

  fclose(file);
  printf("Part 1 - Sum of item priorities:  %d\n", item_sum);
  printf("Part 2 - Sum of badge priorities: %d\n", badge_sum);

  return 0;
}