aoc24/13/main.cc

#include <fstream>
#include <iostream>
#include <sstream>
#include <vector>
#include <tuple>
#include <set>

using namespace std;

#ifdef DEBUG
#define DBG(str) do { std::cout << str << std::endl; } while( false )
#else
#define DBG(str) do { } while ( false )
#endif

vector<vector<int>> parseGames(const char *path) {
  vector<vector<int>> games;

  ifstream input(path);
  string line1;
  string line2;
  string line3;

  while(getline(input, line1)) {
    if (line1 == "") continue;

    vector<int> game;
    getline(input, line2);
    getline(input, line3);

    stringstream ss1;
    stringstream ss2;
    stringstream ss3;
    ss1 << line1;
    ss2 << line2;
    ss3 << line3;

    int a;

    // button A
    char c = 1;
    while(c && c != '+') {
      ss1 >> c;
    }
    ss1 >> a;
    game.push_back(a);

    c = 1;
    while(c && c != '+') {
      ss1 >> c;
    }
    ss1 >> a;
    game.push_back(a);

    // button B
    c = 1;
    while(c && c != '+') {
      ss2 >> c;
    }
    ss2 >> a;
    game.push_back(a);

    c = 1;
    while(c && c != '+') {
      ss2 >> c;
    }
    ss2 >> a;
    game.push_back(a);

    // prize
    c = 1;
    while(c && c != '=') {
      ss3 >> c;
    }
    ss3 >> a;
    game.push_back(a);

    c = 1;
    while(c && c != '=') {
      ss3 >> c;
    }
    ss3 >> a;
    game.push_back(a);

    games.push_back(game);
  }

  return games;
}

// long cheapest = __LONG_MAX__;

// bool playGame(vector<int> game, int as, int bs, int curr_x, int curr_y) {
//   int a_x = game[0];
//   int a_y = game[1];
//   int b_x = game[2];
//   int b_y = game[3];
//   int prize_x = game[4];
//   int prize_y = game[5];

//   bool found_result = false;

//   cout << "curr_x=" << curr_x << " curr_y=" << curr_y << " as=" << as << " bs=" << bs << endl;

//   // base case
//   if (curr_x == prize_x && curr_y == prize_y) {
//     if (as * 3 + bs < cheapest) cheapest = as * 3 + bs;
//     return true;
//   }
//   if (curr_x > prize_x || curr_y > prize_y || as > 100 || bs > 100) return false;

//   // try A
//   if (playGame(game, as + 1, bs, curr_x + a_x, curr_y + a_y)) found_result = true;


//   // try B
//   if (playGame(game, as, bs + 1, curr_x + b_x, curr_y + b_y)) found_result = true;

//   return found_result;
// }

// void printGames(vector<vector<int>> games) {
//   for (auto game : games) {
//     cout << "Button A: X+" << game[0] << ", Y+" << game[1] << endl;
//     cout << "Button B: X+" << game[2] << ", Y+" << game[3] << endl;
//     cout << "Prize: X=" << game[4] << ", Y=" << game[5] << endl;
//     cout << endl;
//   }
// }

unsigned long long playGame(vector<int> game, bool part2 = false) {
  int a_x = game[0];
  int a_y = game[1];
  int b_x = game[2];
  int b_y = game[3];
  unsigned long long prize_x = game[4];
  unsigned long long prize_y = game[5];

  if (!part2) {
    for (long bs = 0; bs < 100; bs++) {
      for (long as = 0; as < 100; as++) {
        if (as * a_x + bs * b_x == prize_x && as * a_y + bs * b_y == prize_y) {
          return 3 * as + bs;
        }
      }
    }
  }

  if (part2) {
    prize_x += 10000000000000l;
    prize_y += 10000000000000l;


    long numeratorX = prize_x*b_y - prize_y*b_x;
    long denominatorX = a_x*b_y - a_y*b_x;
        
    long numeratorY = prize_x*a_y - prize_y*a_x;
    long denominatorY = a_y*b_x - a_x*b_y;

    long a = numeratorX / denominatorX;
    long b = numeratorY / denominatorY;

    if (a * a_x + b * b_x != prize_x || a * a_y + b * b_y != prize_y) return 0;
    return a * 3 + b;
  }
  return 0;
}

int part1(const char *path) {
  vector<vector<int>> games = parseGames(path);
  // printGames(games);

  int tokens = 0;

  for (auto game : games) {
    tokens += playGame(game);
  }

  return tokens;
}

unsigned long long part2(const char *path) {
  vector<vector<int>> games = parseGames(path);

  unsigned long long tokens = 0;

  for (auto game : games) {
    tokens += playGame(game, true);
  }

  return tokens;
}

int main(int argc, char *argv[]) {
  int example1 = part1("example");
  cout << "example1: " << example1 << endl;
  int input1 = part1("input");
  cout << "input1: " << input1 << endl;

  unsigned long long example2 = part2("example");
  cout << "example2: " << example2 << endl;
  unsigned long long input2 = part2("input");
  cout << "input2: " << input2 << endl;
  return 0;
}