SearchHelpers.cs

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// Copyright 2010-2018 Google LLC
// 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.Generic;
 
namespace Google.OrTools.Sat
{
 
  public class CpSolverSolutionCallback : SolutionCallback
  {
    public long Value(LinearExpr e)
    {
      List<LinearExpr> exprs = new List<LinearExpr>();
      List<long> coeffs = new List<long>();
      exprs.Add(e);
      coeffs.Add(1L);
      long constant = 0;
 
      while (exprs.Count > 0)
      {
        LinearExpr expr = exprs[0];
        exprs.RemoveAt(0);
        long coeff = coeffs[0];
        coeffs.RemoveAt(0);
        if (coeff == 0) continue;
 
        if (expr is ProductCst)
        {
          ProductCst p = (ProductCst)expr;
          if (p.Coeff != 0)
          {
            exprs.Add(p.Expr);
            coeffs.Add(p.Coeff * coeff);
          }
        }
        else if (expr is SumArray)
        {
          SumArray a = (SumArray)expr;
          constant += coeff * a.Constant;
          foreach (LinearExpr sub in a.Expressions)
          {
            exprs.Add(sub);
            coeffs.Add(coeff);
          }
        }
        else if (expr is IntVar)
        {
          int index = expr.Index;
          long value = SolutionIntegerValue(index);
          constant += coeff * value;
        }
        else if (expr is NotBooleanVariable)
        {
          throw new ArgumentException(
              "Cannot evaluate a literal in an integer expression.");
        }
        else
        {
          throw new ArgumentException("Cannot evaluate '" + expr.ToString() +
                                      "' in an integer expression");
        }
      }
      return constant;
    }
 
    public Boolean BooleanValue(ILiteral literal)
    {
      if (literal is IntVar || literal is NotBooleanVariable)
      {
        int index = literal.GetIndex();
        return SolutionBooleanValue(index);
      }
      else
      {
        throw new ArgumentException("Cannot evaluate '" + literal.ToString() +
                                    "' as a boolean literal");
      }
    }
  }
 
  public class ObjectiveSolutionPrinter : CpSolverSolutionCallback
  {
    private DateTime _startTime;
    private int _solutionCount;
 
    public ObjectiveSolutionPrinter()
    {
      _startTime = DateTime.Now;
    }
 
    public override void OnSolutionCallback()
    {
      var currentTime = DateTime.Now;
      var objective = ObjectiveValue();
      var objectiveBound = BestObjectiveBound();
      var objLb = Math.Min(objective, objectiveBound);
      var objUb = Math.Max(objective, objectiveBound);
      var time = currentTime - _startTime;
 
      Console.WriteLine(value: $"Solution {_solutionCount}, time = {time.TotalSeconds} s, objective = [{objLb}, {objUb}]");
 
      _solutionCount++;
    }
 
    public int solutionCount() => _solutionCount;
  }
 
}  // namespace Google.OrTools.Sat