024: Langford's number problem

//
// 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.Text.RegularExpressions;
using Google.OrTools.ConstraintSolver;

public class Langford
{

  /**
   *
   * Langford number problem.
   * See http://www.hakank.org/or-tools/langford.py
   *
   */
  private static void Solve(int k = 8, int num_sol = 0)
  {

    Solver solver = new Solver("Langford");

    Console.WriteLine("k: {0}", k);

    //
    // data
    //
    int p = 2*k;

    //
    // Decision variables
    //
    IntVar[] position = solver.MakeIntVarArray(p, 0, p-1, "position");
    IntVar[] solution = solver.MakeIntVarArray(p, 1, k, "solution");

    //
    // Constraints
    //
    solver.Add(position.AllDifferent());

    for(int i = 1; i <= k; i++) {
      solver.Add(position[i+k-1] - (position[i-1] + solver.MakeIntVar(i+1,i+1)) == 0);
      solver.Add(solution.Element(position[i-1]) == i);
      solver.Add(solution.Element(position[k+i-1]) == i);
    }

    // Symmetry breaking
    solver.Add(solution[0] < solution[2*k-1]);

    //
    // Search
    //
    DecisionBuilder db = solver.MakePhase(position,
                                          Solver.CHOOSE_FIRST_UNBOUND,
                                          Solver.ASSIGN_MIN_VALUE);


    solver.NewSearch(db);

    int num_solutions = 0;
    while (solver.NextSolution()) {
      Console.Write("solution : ");
      for(int i = 0; i < p; i++) {
        Console.Write(solution[i].Value() + " ");
      }
      Console.WriteLine();
      num_solutions++;
      if (num_sol > 0 && num_solutions >= num_sol) {
        break;
      }
    }

    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();

  }



  public static void Main(String[] args)
  {
    int k = 8;
    int num_sol = 0; // 0: print all solutions

    if (args.Length > 0) {
      k = Convert.ToInt32(args[0]);
    }

    if (args.Length > 1) {
      num_sol = Convert.ToInt32(args[1]);
    }

    Solve(k, num_sol);

  }
}