mahjong.cpp

// A simple singleplayer mahjong simulator where the player draws from the wall and tries to form four groups and a pair, or seven pairs.

#include <bits/stdc++.h>
using namespace std;

// Source of randomness
mt19937_64 rand_gen(time(0));

const int COUNT = 14;
const vector<pair<int, int>> POSSIBLE_CNTS {{4, 1}, {0, 7}}; // (# groups, # pairs)

class Tile {
  public:
    static const vector<string> num_suits;
    static const vector<string> num_ranks;
    static const vector<string> honor_suits;
    static const vector<string> honor_ranks;
    static const map<string, int> suit_comp;
    static const map<string, int> rank_comp;

    // returns "X" if there is no next rank
    static string next_rank(string rank) {
      char num = rank[0];
      if (num >= '1' && num <= '8') {
        num++;
        return string(1, num);
      } else {
        return "X";
      }
    }
    static Tile to_tile(string str_rep) {
      // string must be non-empty
      if (str_rep.length() == 0) {
        return Tile();
      } else {
        string first_char = str_rep.substr(0, 1);
        if (find(num_ranks.begin(), num_ranks.end(), first_char) == num_ranks.end()) {
          // honor tile
          if (find(honor_ranks.begin(), honor_ranks.end(), str_rep) == honor_ranks.end()) {
            return Tile();
          } else {
            return Tile("h", str_rep);
          }
        } else {
          // numeric tile
          string rest_of_str = str_rep.substr(1);
          if (find(num_suits.begin(), num_suits.end(), rest_of_str) == num_suits.end()) {
            return Tile();
          } else {
            return Tile(rest_of_str, first_char);
          }
        }
      }
    }

    string suit; // m for man, p for pin, s for sou, h for honor. x = invalid suit
    string rank; // 1-9 or N E S W Re Gr Wh. X = invalid rank

    // returns invalid tile by default
    Tile() {
      suit = "x";
      rank = "X";
    }
    Tile(string suit, string rank) {
      this->suit = suit;
      this->rank = rank;
    }

    bool operator==(const Tile& y) {
      return (suit == y.suit) && (rank == y.rank);
    }
    bool operator<(const Tile& y) {
      pair<int, int> cur_id {suit_comp.at(suit), rank_comp.at(rank)};
      pair<int, int> other_id {suit_comp.at(y.suit), rank_comp.at(y.rank)};
      return cur_id < other_id;
    }
    string to_str() {
      if (suit == "h") {
        return rank;
      } else {
        return rank + suit;
      }
    }
};
const vector<string> Tile::num_suits {"m", "p", "s"};
const vector<string> Tile::num_ranks {"1", "2", "3", "4", "5", "6", "7", "8", "9"};
const vector<string> Tile::honor_suits {"h"};
const vector<string> Tile::honor_ranks {"N", "E", "S", "W", "Wh", "Gr", "Re"};
const map<string, int> Tile::suit_comp {
  {"m", 1},
  {"p", 2},
  {"s", 3},
  {"h", 4}
};
const map<string, int> Tile::rank_comp {
  {"1", 1},
  {"2", 2},
  {"3", 3},
  {"4", 4},
  {"5", 5},
  {"6", 6},
  {"7", 7},
  {"8", 8},
  {"9", 9},
  {"N", 10},
  {"E", 11},
  {"S", 12},
  {"W", 13},
  {"Wh", 14},
  {"Gr", 15},
  {"Re", 16}
};

class Hand {
  public:
    vector<Tile> tiles;

    Hand() {
      this->tiles = vector<Tile>();
    }
    Hand(vector<Tile>& tiles) {
      this->tiles = vector<Tile>(tiles);
    }

    void shuffle() {
      std::shuffle(tiles.begin(), tiles.end(), rand_gen);
    }
    void insert(Tile t) {
      tiles.push_back(t);
      sort(tiles.begin(), tiles.end());
    }
    bool contains(Tile t) {
      return find(tiles.begin(), tiles.end(), t) != tiles.end();
    }
    bool remove(Tile t) {
      if (contains(t)) {
        tiles.erase(find(tiles.begin(), tiles.end(), t));
        return true;
      } else {
        return false;
      }
    }
    bool complete() {
      if (tiles.size() != COUNT) return false;
      // Recursive search to find all possibilities for (group count, pair count)
      set<pair<int, int>> cnt_possible;
      // DFS stack
      vector<pair<Hand, pair<int, int>>> dfs;
      dfs.push_back({*this, {0, 0}});
      while (!dfs.empty()) {
        auto cur = dfs.back();
        dfs.pop_back();
        Hand cur_hand = cur.first;
        int cur_g_cnt, cur_p_cnt;
        tie(cur_g_cnt, cur_p_cnt) = cur.second;
        // If we processed the entire hand
        if (cur_hand.tiles.empty()) {
          cnt_possible.insert({cur_g_cnt, cur_p_cnt});
        } else {
          // Make a group or pair with the first tile
          Tile first = cur_hand.tiles[0];
          cur_hand.remove(first);
          Hand hand_copy = cur_hand;
          // Check for a pair
          if (hand_copy.remove(first)) {
            dfs.push_back({hand_copy, {cur_g_cnt, cur_p_cnt + 1}});
            // Check for a triplet
            if (hand_copy.remove(first)) {
              dfs.push_back({hand_copy, {cur_g_cnt + 1, cur_p_cnt}});
            }
          }
          // Check for a sequence
          string second_rank = Tile::next_rank(first.rank);
          string third_rank = Tile::next_rank(second_rank);
          Tile second = Tile(first.suit, second_rank);
          Tile third = Tile(first.suit, third_rank);
          if (cur_hand.remove(second) && cur_hand.remove(third)) {
            dfs.push_back({cur_hand, {cur_g_cnt + 1, cur_p_cnt}});
          }
        }
      }
      // Check all cases in POSSIBLE_CNTS
      for (auto good_cnt : POSSIBLE_CNTS) {
        if (cnt_possible.count(good_cnt)) return true;
      }
      return false;
    }
    string to_str() {
      string output = "";
      for (Tile t : tiles) {
        output += t.to_str() + " ";
      }
      return output;
    }
};

int main() {
  // make the wall
  Hand wall = Hand();
  for (string s : Tile::num_suits) {
    for (string r : Tile::num_ranks) {
      for (int i = 0; i < 4; i++) {
        wall.insert(Tile(s, r));
      }
    }
  }
  for (string s : Tile::honor_suits) {
    for (string r : Tile::honor_ranks) {
      for (int i = 0; i < 4; i++) {
        wall.insert(Tile(s, r));
      }
    }
  }
  wall.shuffle();
  // Choose the dora indicator
  Tile dora_ind = wall.tiles[0];
  auto next_tile = wall.tiles.begin() + 1;
  // Make the player's starting hand
  Hand player_hand = Hand();
  for (int i = 0; i < 13; i++) {
    player_hand.insert(*next_tile);
    next_tile++;
  }
  // Game Loop
  bool hand_completed = false;
  bool riichi = false;
  int turn = 0;
  Tile draw;

  for (; next_tile != wall.tiles.end(); turn++) {
    draw = *next_tile;
    next_tile++;
    cout << "Turn " << turn << endl;
    cout << "Dora Indicator: " << dora_ind.to_str() << endl;
    cout << "Your Hand:" << endl;
    cout << player_hand.to_str() << "| " << draw.to_str() << "\n";
    player_hand.insert(draw);

    while (true) {
      cout << "Enter move: ";
      string action;
      cin >> action;
      // Riichi action
      if (action == ">>") {
        cin >> action;
        Tile discard = Tile::to_tile(action);
        if (player_hand.contains(discard)) {
          player_hand.remove(discard);
          riichi = true;
          break;
        } else {
          cout << "Invalid move!" << endl;
        }
      }
      // Check if hand is complete
      else if (action == "!") {
        if (player_hand.complete()) {
          hand_completed = true;
          break;
        } else {
          cout << "Invalid move!" << endl;
        }
      }
      // Regular discard
      else {
        Tile discard = Tile::to_tile(action);
        if (player_hand.contains(discard)) {
          player_hand.remove(discard);
          break;
        } else {
          cout << "Invalid move!" << endl;
        }
      }
    }
    cout << endl;
    if (riichi || hand_completed) break;
  }
  // Riichi fast-forward
  if (riichi) {
    turn++;
    for (; next_tile != wall.tiles.end(); turn++) {
      draw = *next_tile;
      next_tile++;
      player_hand.insert(draw);
      if (player_hand.complete()) {
        hand_completed = true;
        break;
      } else {
        player_hand.remove(draw);
      }
    }
  }
  if (hand_completed) {
    player_hand.remove(draw);
    cout << "| " << player_hand.to_str() << "| " << draw.to_str() << " |" << endl;
    cout << "You completed your hand in " << turn << " turns. Congratulations!" << endl;
    cout << endl;
    cout << "                                       :-:::::::                        :::                         \n"
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      "==================:@#::-=====@%###########%#=:::::#...   .....=+...  ..:::::::-@====================\n";
  } else {
    cout << "You ran out of tiles!" << endl;
  }
}