minesweeper.cs

//
// Copyright 2012 Hakan Kjellerstrand
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

using System;
using System.Collections;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using Google.OrTools.ConstraintSolver;


public class Minesweeper
{

  static int X = -1;

  //
  // Default problem.
  // It has 4 solutions.
  //
  static int default_r = 8;
  static int default_c = 8;
  static int[,] default_game =  {{2, 3, X, 2, 2, X, 2, 1},
                                 {X, X, 4, X, X, 4, X, 2},
                                 {X, X, X, X, X, X, 4, X},
                                 {X, 5, X, 6, X, X, X, 2},
                                 {2, X, X, X, 5, 5, X, 2},
                                 {1, 3, 4, X, X, X, 4, X},
                                 {0, 1, X, 4, X, X, X, 3},
                                 {0, 1, 2, X, 2, 3, X, 2}};

  // for the actual problem
  static int r;
  static int c;
  static int[,] game;


  /**
   *
   * Solves the Minesweeper problems.
   *
   * See http://www.hakank.org/google_or_tools/minesweeper.py
   *
   */
  private static void Solve()
  {
    Solver solver = new Solver("Minesweeper");

    //
    // data
    //
    int[] S = {-1, 0, 1};

    Console.WriteLine("Problem:");
    for(int i = 0; i < r; i++) {
      for(int j = 0; j < c; j++) {
        if (game[i,j] > X) {
          Console.Write(game[i,j] + " ");
        } else {
          Console.Write("X ");
        }
      }
      Console.WriteLine();
    }
    Console.WriteLine();


    //
    // Decision variables
    //
    IntVar[,] mines = solver.MakeIntVarMatrix(r, c, 0, 1, "mines");
    // for branching
    IntVar[] mines_flat = mines.Flatten();

    //
    // Constraints
    //  
    for(int i = 0; i < r; i++) {
      for(int j = 0; j < c; j++) {
        if (game[i,j] >= 0) {
          solver.Add( mines[i,j] == 0);

          // this cell is the sum of all its neighbours
          var tmp = from a in S from b in S where 
            i + a >= 0 &&
            j + b >= 0 &&
            i + a < r &&
            j + b < c
            select(mines[i+a,j+b]);

          solver.Add(tmp.ToArray().Sum() == game[i,j]);

        }

        if (game[i,j] > X) {
          // This cell cannot be a mine since it 
          // has some value assigned to it
          solver.Add(mines[i,j] == 0);
        }
      }
    }


    //
    // Search
    //
    DecisionBuilder db = solver.MakePhase(mines_flat,
                                          Solver.CHOOSE_PATH,
                                          Solver.ASSIGN_MIN_VALUE);

    solver.NewSearch(db);

    int sol = 0;
    while (solver.NextSolution()) {
      sol++;
      Console.WriteLine("Solution #{0} ", sol + " ");
      for(int i = 0; i < r; i++) {
        for(int j = 0; j < c; j++){ 
          Console.Write("{0} ", mines[i,j].Value());
        }
        Console.WriteLine();
      }
      
      Console.WriteLine();
    }

    Console.WriteLine("\nSolutions: {0}", solver.Solutions());
    Console.WriteLine("WallTime: {0}ms", solver.WallTime());
    Console.WriteLine("Failures: {0}", solver.Failures());
    Console.WriteLine("Branches: {0} ", solver.Branches());

    solver.EndSearch();

  }

  /**
   *
   * Reads a minesweeper file.
   * File format:
   *  # a comment which is ignored
   *  % a comment which also is ignored
   *  number of rows
   *  number of columns
   *  <
   *    row number of neighbours lines...
   *  >
   * 
   * 0..8 means number of neighbours, "." mean unknown (may be a mine)
   * 
   * Example (from minesweeper0.txt)
   * # Problem from Gecode/examples/minesweeper.cc  problem 0
   * 6
   * 6
   * ..2.3.
   * 2.....
   * ..24.3
   * 1.34..
   * .....3
   * .3.3..
   *
   */
  private static void readFile(String file) {

    Console.WriteLine("readFile(" + file + ")");
    int lineCount = 0;
        
    TextReader inr = new StreamReader(file);
    String str;
    while ((str = inr.ReadLine()) != null && str.Length > 0) {
      
      str = str.Trim();
      
      // ignore comments
      if(str.StartsWith("#") || str.StartsWith("%")) {
        continue;
      }
      
      Console.WriteLine(str);
      if (lineCount == 0) {
        r = Convert.ToInt32(str); // number of rows
      } else if (lineCount == 1) {
        c = Convert.ToInt32(str); // number of columns
        game = new int[r,c];
      } else {
        // the problem matrix
        String[] row = Regex.Split(str, "");
        for(int j = 1; j <= c; j++) {
          String s = row[j];
          if (s.Equals(".")) {
            game[lineCount-2,j-1] = -1;
          } else {
            game[lineCount-2,j-1] = Convert.ToInt32(s);
          }
        }
      }
      
      lineCount++;
      
    } // end while
    
    inr.Close();
    
  } // end readFile


  public static void Main(String[] args)
  {
    String file = "";
    if (args.Length > 0) {
      file = args[0];
      readFile(file);
    } else {
      game = default_game;
      r = default_r;
      c = default_c;
    }

    Solve();
  }
}