The Connected Four game.

Hamlet.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Text.RegularExpressions;
using Internal;

enum Cell {
  Empty,
  Black,
  White,
}

class Board {
  Cell[, ] cells;

  Action<Player> onGameSet;

  public Board(int width, int height, Action<Player> gameSet) {
    cells = new Cell[width, height];

    onGameSet = gameSet;

    for (int y = 0; y < cells.GetLength(1); ++y) {
      for (int x = 0; x < cells.GetLength(0); ++x) {
        cells[x, y] = Cell.Empty;
      }
    }
  }

  Player PlayerFrom(Cell cell) {
    if (cell == Cell.Black) {
      return Player.Black;
    }
    if (cell == Cell.White) {
      return Player.White;
    }
    throw new Exception("Illegal cell state");
  }

  int CountSeq(Cell target, int x, int y, int vx, int vy) {
    var looking = GetCell(x + vx, y + vy);
    if (looking != target) {
      return 0;
    }
    return 1 + CountSeq(target, x + vx, y + vy, vx, vy);
  }

  void CheckCellsFilled() {
    for (int y = 0; y < cells.GetLength(1); ++y) {
      for (int x = 0; x < cells.GetLength(0); ++x) {
        if (cells[x, y] == Cell.Empty) {
          return;
        }
      }
    }
    onGameSet(Player.Draw);
  }

  void Judge(int x, int y) {
    var current = GetCell(x, y);
    if (current == Cell.Empty) { return; }

    var xDirCount = CountSeq(current, x, y, 1, 0) + CountSeq(current, x, y, -1, 0);
    var yDirCount = CountSeq(current, x, y, 0, 1) + CountSeq(current, x, y, 0, -1);
    var xyDirCount = CountSeq(current, x, y, 1, 1) + CountSeq(current, x, y, -1, -1);
    var x_yDirCount = CountSeq(current, x, y, 1, -1) + CountSeq(current, x, y, -1, 1);

    if (3 <= xDirCount || 3 <= yDirCount || 3 <= xyDirCount || 3 <= x_yDirCount) {
      onGameSet(PlayerFrom(current));
    }

    CheckCellsFilled();
  }

  public Cell GetCell(int x, int y) {
    if (!(0 <= x && x < cells.GetLength(0) &&
        0 <= y && y < cells.GetLength(1))) {
      return Cell.Empty;
    }
    return cells[x, y];
  }

  public void FallCell(Cell cell, int x) {
    if (!(0 <= x && x < cells.GetLength(0))) {
      throw new ArgumentOutOfRangeException("");
    }

    for (int y = 0; y < cells.GetLength(1); ++y) {
      if (cells[x, y] == Cell.Empty) {
        cells[x, y] = cell;
        Judge(x, y);
        return;
      }
    }
    throw new OverflowException("");
  }
}

enum Player {
  Black,
  White,
  Draw,
}

class GameView {
  Board board;
  bool playing;
  Player player;

  readonly int W;
  readonly int H;

  public GameView(int width, int height) {
    board = new Board(width, height, this.GameSet);
    player = Player.Black;

    W = width;
    H = height;
  }

  void GameSet(Player winner) {
    Flush();

    if (winner == Player.Draw) {
      Console.WriteLine("引き分け!");
    } else {
      Console.WriteLine("{0}の勝利!", PlayerName());
    }
    playing = false;
  }

  void StartGame() {
    playing = true;
  }

  void Flush() {
    Console.Clear();

    // Positions
    for (int x = 0; x < W; ++x) {
      Console.Write(" {0}", x);
    }
    Console.WriteLine();

    // Cells
    for (int y = H - 1; 0 <= y; --y) {
      for (int x = 0; x < W; ++x) {
        var cellChar = "_";
        switch (board.GetCell(x, y)) {
          case Cell.Black:
            cellChar = "■";
            break;
          case Cell.White:
            cellChar = "○";
            break;
        }
        Console.Write(" {0}", cellChar);
      }
      Console.WriteLine();
    }
  }

  string PlayerName() {
    if (player == Player.White) {
      return "白";
    }
    if (player == Player.Black) {
      return "黒";
    }
    return "謎の人物";
  }

  void AskCommand() {
    Console.WriteLine("{0}の手番です。石を落とす位置を入力してね", PlayerName());

    while (true) {
      try {
        int pos = int.Parse(Console.ReadLine());
        Cell toFall = Cell.Empty;
        if (player == Player.Black) {
          toFall = Cell.Black;
        } else if (player == Player.White) {
          toFall = Cell.White;
        }
        board.FallCell(toFall, pos);
        break;
      } catch (OverflowException _e) {
        Console.WriteLine("空いている列を選んでね");
      } catch (Exception _ignore) {
        Console.WriteLine("上の範囲内の数字で入力し直してね");
      }
    }
  }

  void NextTurn() {
    if (player == Player.Black) {
      player = Player.White;
    } else if (player == Player.White) {
      player = Player.Black;
    }
  }

  public void Run() {
    StartGame();
    while (playing) {
      Flush();
      AskCommand();
      NextTurn();
    }
  }
}

class Hamlet {
  static int Main() {
    var view = new GameView(8, 8);
    view.Run();
    return 0;
  }
}