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

int part_1(FILE *input) {
  rewind(input);
  char polymer[50001];
  fread(polymer, 50000, 1, input);
  bool changed = true;
  while(changed) {
    changed = false;
    for(int i = 0; i < 50000; i++) {
      if(polymer[i] == ' ') continue;

      for(int j = i + 1; j < 50000; j++) {
	if(polymer[j] == ' ') continue;

	if(polymer[i] == (polymer[j] + 'a' - 'A') || polymer[i] == (polymer[j] + 'A' - 'a') ) {
	  polymer[i] = ' ';
	  polymer[j] = ' ';
	  changed = true;
	}
	break;
      }
    }
  }

  int count = 0;
  for(int i = 0; i < 50000; i++) {
    if(polymer[i] != ' ') count++;
  }
  
  return count;
}

int part_2(FILE *input) {
  char polymer[50001];
  int best_count = 50000;
  for(char to_remove = 'a'; to_remove <= 'z'; to_remove++) {
    rewind(input);
    fread(polymer, 50000, 1, input);

    for(int i = 0; i < 50000; i++) {
      if(polymer[i] == to_remove || polymer[i] == to_remove - 'a' + 'A') polymer[i] = ' ';
    }

    bool changed = true;
    while(changed) {
      changed = false;
      for(int i = 0; i < 50000; i++) {
	if(polymer[i] == ' ') continue;

	for(int j = i + 1; j < 50000; j++) {
	  if(polymer[j] == ' ') continue;

	  if(polymer[i] == (polymer[j] + 'a' - 'A') || polymer[i] == (polymer[j] + 'A' - 'a') ) {
	    polymer[i] = ' ';
	    polymer[j] = ' ';
	    changed = true;
	  }
	  break;
	}
      }
    }

    int count = 0;
    for(int i = 0; i < 50000; i++) {
      if(polymer[i] != ' ') count++;
    }

    if(count < best_count) best_count = count;
  }
  
  return best_count;
}

int main() {
  char *input_file_path = "../data/2018/5/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);
}