solve day 13

13/example

@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279

13/main.cc

@@ -0,0 +1,205 @@
+#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;
+}