CpModel.cs

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// Copyright 2010-2022 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.
 
namespace Google.OrTools.Sat
{
using System;
using System.Collections.Generic;
using Google.OrTools.Util;
 
public class CpModel
{
    public CpModel()
    {
        model_ = new CpModelProto();
        constant_map_ = new Dictionary<long, int>();
        var_value_map_ = new Dictionary<int, long>(10);
        terms_ = new Queue<Term>(10);
    }
 
    // Getters.
 
    public CpModelProto Model
    {
        get {
            return model_;
        }
    }
 
    int Negated(int index)
    {
        return -index - 1;
    }
 
    // Integer variables and constraints.
 
    public IntVar NewIntVar(long lb, long ub, string name)
    {
        return new IntVar(model_, lb, ub, name);
    }
 
    public IntVar NewIntVarFromDomain(Domain domain, string name)
    {
        return new IntVar(model_, domain, name);
    }
 
    public IntVar NewConstant(long value)
    {
        return new IntVar(model_, ConvertConstant(value));
    }
 
    public BoolVar NewBoolVar(string name)
    {
        return new BoolVar(model_, name);
    }
 
    public ILiteral TrueLiteral()
    {
        return true_literal_ ??= new BoolVar(model_, ConvertConstant(1));
    }
 
    public ILiteral FalseLiteral()
    {
        return TrueLiteral().Not();
    }
 
    private long FillLinearConstraint(LinearExpr expr, out LinearConstraintProto linear)
    {
        var dict = var_value_map_;
        dict.Clear();
        long constant = LinearExpr.GetVarValueMap(expr, dict, terms_);
        var count = dict.Count;
        linear = new LinearConstraintProto();
        linear.Vars.Capacity = count;
        linear.Vars.AddRange(dict.Keys);
        linear.Coeffs.Capacity = count;
        linear.Coeffs.AddRange(dict.Values);
        return constant;
    }
    public Constraint AddLinearConstraint(LinearExpr expr, long lb, long ub)
    {
        long constant = FillLinearConstraint(expr, out var linear);
        linear.Domain.Capacity = 2;
        linear.Domain.Add(lb is Int64.MinValue or Int64.MaxValue ? lb : lb - constant);
        linear.Domain.Add(ub is Int64.MinValue or Int64.MaxValue ? ub : ub - constant);
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Linear = linear;
        return ct;
    }
 
    public Constraint AddLinearExpressionInDomain(LinearExpr expr, Domain domain)
    {
        long constant = FillLinearConstraint(expr, out var linear);
        var array = domain.FlattenedIntervals();
        linear.Domain.Capacity = array.Length;
        foreach (long value in array)
        {
            linear.Domain.Add(value is Int64.MinValue or Int64.MaxValue ? value : value - constant);
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Linear = linear;
        return ct;
    }
 
    private Constraint AddLinearExpressionNotEqualCst(LinearExpr expr, long value)
    {
        long constant = FillLinearConstraint(expr, out var linear);
        linear.Domain.Capacity = 4;
        linear.Domain.Add(Int64.MinValue);
        linear.Domain.Add(value - constant - 1);
        linear.Domain.Add(value - constant + 1);
        linear.Domain.Add(Int64.MaxValue);
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Linear = linear;
        return ct;
    }
 
    public Constraint Add(BoundedLinearExpression lin)
    {
        switch (lin.CtType)
        {
        case BoundedLinearExpression.Type.BoundExpression: {
            return AddLinearConstraint(lin.Left, lin.Lb, lin.Ub);
        }
        case BoundedLinearExpression.Type.VarEqVar: {
            return AddLinearConstraint(lin.Left - lin.Right, 0, 0);
        }
        case BoundedLinearExpression.Type.VarDiffVar: {
            return AddLinearExpressionNotEqualCst(lin.Left - lin.Right, 0);
        }
        case BoundedLinearExpression.Type.VarEqCst: {
            return AddLinearConstraint(lin.Left, lin.Lb, lin.Lb);
        }
        case BoundedLinearExpression.Type.VarDiffCst: {
            return AddLinearExpressionNotEqualCst(lin.Left, lin.Lb);
        }
        }
        return null;
    }
 
    public Constraint AddAllDifferent(IEnumerable<LinearExpr> exprs)
    {
        AllDifferentConstraintProto alldiff = new AllDifferentConstraintProto();
        alldiff.Exprs.TrySetCapacity(exprs);
        foreach (LinearExpr expr in exprs)
        {
            alldiff.Exprs.Add(GetLinearExpressionProto(expr));
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.AllDiff = alldiff;
        return ct;
    }
 
    public Constraint AddElement(IntVar index, IEnumerable<IntVar> vars, IntVar target)
    {
        ElementConstraintProto element = new ElementConstraintProto();
        element.Index = index.Index;
        element.Vars.TrySetCapacity(vars);
        foreach (IntVar var in vars)
        {
            element.Vars.Add(var.Index);
        }
        element.Target = target.Index;
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Element = element;
        return ct;
    }
 
    public Constraint AddElement(IntVar index, IEnumerable<long> values, IntVar target)
    {
        ElementConstraintProto element = new ElementConstraintProto();
        element.Index = index.Index;
        element.Vars.TrySetCapacity(values);
        foreach (long value in values)
        {
            element.Vars.Add(ConvertConstant(value));
        }
        element.Target = target.Index;
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Element = element;
        return ct;
    }
 
    public Constraint AddElement(IntVar index, IEnumerable<int> values, IntVar target)
    {
        ElementConstraintProto element = new ElementConstraintProto();
        element.Index = index.Index;
        element.Vars.TrySetCapacity(values);
        foreach (int value in values)
        {
            element.Vars.Add(ConvertConstant(value));
        }
        element.Target = target.Index;
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Element = element;
        return ct;
    }
 
    public CircuitConstraint AddCircuit()
    {
        CircuitConstraint ct = new CircuitConstraint(model_);
        ct.Proto.Circuit = new CircuitConstraintProto();
        return ct;
    }
 
    public MultipleCircuitConstraint AddMultipleCircuit()
    {
        MultipleCircuitConstraint ct = new MultipleCircuitConstraint(model_);
        ct.Proto.Routes = new RoutesConstraintProto();
        return ct;
    }
 
    public TableConstraint AddAllowedAssignments(IEnumerable<IntVar> vars)
    {
        TableConstraintProto table = new TableConstraintProto();
        table.Vars.TrySetCapacity(vars);
        foreach (IntVar var in vars)
        {
            table.Vars.Add(var.Index);
        }
 
        TableConstraint ct = new TableConstraint(model_);
        ct.Proto.Table = table;
        return ct;
    }
 
    public TableConstraint AddForbiddenAssignments(IEnumerable<IntVar> vars)
    {
        TableConstraint ct = AddAllowedAssignments(vars);
        ct.Proto.Table.Negated = true;
        return ct;
    }
 
    public AutomatonConstraint AddAutomaton(IEnumerable<IntVar> vars, long starting_state,
                                            IEnumerable<long> final_states)
    {
        AutomatonConstraintProto aut = new AutomatonConstraintProto();
        aut.Vars.TrySetCapacity(vars);
        foreach (IntVar var in vars)
        {
            aut.Vars.Add(var.Index);
        }
 
        aut.StartingState = starting_state;
        aut.FinalStates.AddRange(final_states);
 
        AutomatonConstraint ct = new AutomatonConstraint(model_);
        ct.Proto.Automaton = aut;
        return ct;
    }
 
    public Constraint AddInverse(IEnumerable<IntVar> direct, IEnumerable<IntVar> reverse)
    {
        InverseConstraintProto inverse = new InverseConstraintProto();
        inverse.FDirect.TrySetCapacity(direct);
        foreach (IntVar var in direct)
        {
            inverse.FDirect.Add(var.Index);
        }
 
        inverse.FInverse.TrySetCapacity(reverse);
        foreach (IntVar var in reverse)
        {
            inverse.FInverse.Add(var.Index);
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.Inverse = inverse;
        return ct;
    }
 
    public ReservoirConstraint AddReservoirConstraint(long minLevel, long maxLevel)
    {
        ReservoirConstraintProto res = new ReservoirConstraintProto();
 
        res.MinLevel = minLevel;
        res.MaxLevel = maxLevel;
 
        ReservoirConstraint ct = new ReservoirConstraint(this, model_);
        ct.Proto.Reservoir = res;
        return ct;
    }
 
    public void AddMapDomain(IntVar var, IEnumerable<IntVar> bool_vars, long offset = 0)
    {
        int i = 0;
        int var_index = var.Index;
        foreach (IntVar bool_var in bool_vars)
        {
            int b_index = bool_var.Index;
 
            LinearConstraintProto lin1 = new LinearConstraintProto();
            lin1.Vars.Capacity = 1;
            lin1.Vars.Add(var_index);
            lin1.Coeffs.Capacity = 1;
            lin1.Coeffs.Add(1L);
            lin1.Domain.Capacity = 2;
            lin1.Domain.Add(offset + i);
            lin1.Domain.Add(offset + i);
            ConstraintProto ct1 = new ConstraintProto();
            ct1.Linear = lin1;
            ct1.EnforcementLiteral.Add(b_index);
            model_.Constraints.Add(ct1);
 
            LinearConstraintProto lin2 = new LinearConstraintProto();
            lin1.Vars.Capacity = 1;
            lin2.Vars.Add(var_index);
            lin1.Coeffs.Capacity = 1;
            lin2.Coeffs.Add(1L);
            lin1.Domain.Capacity = 4;
            lin2.Domain.Add(Int64.MinValue);
            lin2.Domain.Add(offset + i - 1);
            lin2.Domain.Add(offset + i + 1);
            lin2.Domain.Add(Int64.MaxValue);
            ConstraintProto ct2 = new ConstraintProto();
            ct2.Linear = lin2;
            ct2.EnforcementLiteral.Add(-b_index - 1);
            model_.Constraints.Add(ct2);
 
            i++;
        }
    }
 
    public Constraint AddImplication(ILiteral a, ILiteral b)
    {
        BoolArgumentProto or = new BoolArgumentProto();
        or.Literals.Capacity = 2;
        or.Literals.Add(a.Not().GetIndex());
        or.Literals.Add(b.GetIndex());
 
        Constraint ct = new Constraint(model_);
        ct.Proto.BoolOr = or;
        return ct;
    }
 
    public Constraint AddBoolOr(IEnumerable<ILiteral> literals)
    {
        BoolArgumentProto bool_argument = new BoolArgumentProto();
        bool_argument.Literals.TrySetCapacity(literals);
        foreach (ILiteral lit in literals)
        {
            bool_argument.Literals.Add(lit.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.BoolOr = bool_argument;
        return ct;
    }
 
    public Constraint AddAtLeastOne(IEnumerable<ILiteral> literals)
    {
        return AddBoolOr(literals);
    }
 
    public Constraint AddAtMostOne(IEnumerable<ILiteral> literals)
    {
        BoolArgumentProto bool_argument = new BoolArgumentProto();
        bool_argument.Literals.TrySetCapacity(literals);
        foreach (ILiteral lit in literals)
        {
            bool_argument.Literals.Add(lit.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.AtMostOne = bool_argument;
        return ct;
    }
 
    public Constraint AddExactlyOne(IEnumerable<ILiteral> literals)
    {
        BoolArgumentProto bool_argument = new BoolArgumentProto();
        bool_argument.Literals.TrySetCapacity(literals);
        foreach (ILiteral lit in literals)
        {
            bool_argument.Literals.Add(lit.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.ExactlyOne = bool_argument;
        return ct;
    }
 
    public Constraint AddBoolAnd(IEnumerable<ILiteral> literals)
    {
        BoolArgumentProto bool_argument = new BoolArgumentProto();
        bool_argument.Literals.TrySetCapacity(literals);
        foreach (ILiteral lit in literals)
        {
            bool_argument.Literals.Add(lit.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.BoolAnd = bool_argument;
        return ct;
    }
 
    public Constraint AddBoolXor(IEnumerable<ILiteral> literals)
    {
        BoolArgumentProto bool_argument = new BoolArgumentProto();
        bool_argument.Literals.TrySetCapacity(literals);
        foreach (ILiteral lit in literals)
        {
            bool_argument.Literals.Add(lit.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.BoolXor = bool_argument;
        return ct;
    }
 
    public Constraint AddMinEquality(LinearExpr target, IEnumerable<LinearExpr> exprs)
    {
        LinearArgumentProto lin = new LinearArgumentProto();
        lin.Exprs.TrySetCapacity(exprs);
        foreach (LinearExpr expr in exprs)
        {
            lin.Exprs.Add(GetLinearExpressionProto(expr, /*negate=*/true));
        }
        lin.Target = GetLinearExpressionProto(target, /*negate=*/true);
 
        Constraint ct = new Constraint(model_);
        ct.Proto.LinMax = lin;
        return ct;
    }
 
    public Constraint AddMaxEquality(LinearExpr target, IEnumerable<LinearExpr> exprs)
    {
        LinearArgumentProto lin = new LinearArgumentProto();
        lin.Exprs.TrySetCapacity(exprs);
        foreach (LinearExpr expr in exprs)
        {
            lin.Exprs.Add(GetLinearExpressionProto(expr));
        }
        lin.Target = GetLinearExpressionProto(target);
 
        Constraint ct = new Constraint(model_);
        ct.Proto.LinMax = lin;
        return ct;
    }
 
    public Constraint AddDivisionEquality<T, N, D>(T target, N num, D denom)
    {
        LinearArgumentProto div = new LinearArgumentProto();
        div.Exprs.Capacity = 2;
        div.Exprs.Add(GetLinearExpressionProto(GetLinearExpr(num)));
        div.Exprs.Add(GetLinearExpressionProto(GetLinearExpr(denom)));
        div.Target = GetLinearExpressionProto(GetLinearExpr(target));
 
        Constraint ct = new Constraint(model_);
        ct.Proto.IntDiv = div;
        return ct;
    }
 
    public Constraint AddAbsEquality(LinearExpr target, LinearExpr expr)
    {
        LinearArgumentProto abs = new LinearArgumentProto();
        abs.Exprs.Capacity = 2;
        abs.Exprs.Add(GetLinearExpressionProto(expr));
        abs.Exprs.Add(GetLinearExpressionProto(expr, /*negate=*/true));
        abs.Target = GetLinearExpressionProto(target);
 
        Constraint ct = new Constraint(model_);
        ct.Proto.LinMax = abs;
        return ct;
    }
 
    public Constraint AddModuloEquality<T, V, M>(T target, V v, M m)
    {
        LinearArgumentProto mod = new LinearArgumentProto();
        mod.Exprs.Capacity = 2;
        mod.Exprs.Add(GetLinearExpressionProto(GetLinearExpr(v)));
        mod.Exprs.Add(GetLinearExpressionProto(GetLinearExpr(m)));
        mod.Target = GetLinearExpressionProto(GetLinearExpr(target));
 
        Constraint ct = new Constraint(model_);
        ct.Proto.IntMod = mod;
        return ct;
    }
 
    public Constraint AddMultiplicationEquality(LinearExpr target, IEnumerable<LinearExpr> exprs)
    {
        LinearArgumentProto prod = new LinearArgumentProto();
        prod.Target = GetLinearExpressionProto(target);
        prod.Exprs.TrySetCapacity(exprs);
        foreach (LinearExpr expr in exprs)
        {
            prod.Exprs.Add(GetLinearExpressionProto(expr));
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.IntProd = prod;
        return ct;
    }
 
    public Constraint AddMultiplicationEquality(LinearExpr target, LinearExpr left, LinearExpr right)
    {
        LinearArgumentProto prod = new LinearArgumentProto();
        prod.Target = GetLinearExpressionProto(target);
        prod.Exprs.Capacity = 2;
        prod.Exprs.Add(GetLinearExpressionProto(left));
        prod.Exprs.Add(GetLinearExpressionProto(right));
 
        Constraint ct = new Constraint(model_);
        ct.Proto.IntProd = prod;
        return ct;
    }
 
    // Scheduling support
 
    public IntervalVar NewIntervalVar<S, D, E>(S start, D size, E end, string name)
    {
        LinearExpr startExpr = GetLinearExpr(start);
        LinearExpr sizeExpr = GetLinearExpr(size);
        LinearExpr endExpr = GetLinearExpr(end);
        Add(startExpr + sizeExpr == endExpr);
 
        LinearExpressionProto startProto = GetLinearExpressionProto(startExpr);
        LinearExpressionProto sizeProto = GetLinearExpressionProto(sizeExpr);
        LinearExpressionProto endProto = GetLinearExpressionProto(endExpr);
        return new IntervalVar(model_, startProto, sizeProto, endProto, name);
    }
 
    public IntervalVar NewFixedSizeIntervalVar<S>(S start, long size, string name)
    {
        LinearExpr startExpr = GetLinearExpr(start);
        LinearExpr sizeExpr = GetLinearExpr(size);
        LinearExpr endExpr = LinearExpr.Sum(new LinearExpr[] { startExpr, sizeExpr });
 
        LinearExpressionProto startProto = GetLinearExpressionProto(startExpr);
        LinearExpressionProto sizeProto = GetLinearExpressionProto(sizeExpr);
        LinearExpressionProto endProto = GetLinearExpressionProto(endExpr);
        return new IntervalVar(model_, startProto, sizeProto, endProto, name);
    }
 
    public IntervalVar NewOptionalIntervalVar<S, D, E>(S start, D size, E end, ILiteral is_present, string name)
    {
        LinearExpr startExpr = GetLinearExpr(start);
        LinearExpr sizeExpr = GetLinearExpr(size);
        LinearExpr endExpr = GetLinearExpr(end);
        Add(startExpr + sizeExpr == endExpr).OnlyEnforceIf(is_present);
 
        LinearExpressionProto startProto = GetLinearExpressionProto(startExpr);
        LinearExpressionProto sizeProto = GetLinearExpressionProto(sizeExpr);
        LinearExpressionProto endProto = GetLinearExpressionProto(endExpr);
        return new IntervalVar(model_, startProto, sizeProto, endProto, is_present.GetIndex(), name);
    }
 
    public IntervalVar NewOptionalFixedSizeIntervalVar<S>(S start, long size, ILiteral is_present, string name)
    {
        LinearExpr startExpr = GetLinearExpr(start);
        LinearExpr sizeExpr = GetLinearExpr(size);
        LinearExpr endExpr = LinearExpr.Sum(new LinearExpr[] { startExpr, sizeExpr });
 
        LinearExpressionProto startProto = GetLinearExpressionProto(startExpr);
        LinearExpressionProto sizeProto = GetLinearExpressionProto(sizeExpr);
        LinearExpressionProto endProto = GetLinearExpressionProto(endExpr);
        return new IntervalVar(model_, startProto, sizeProto, endProto, is_present.GetIndex(), name);
    }
 
    public Constraint AddNoOverlap(IEnumerable<IntervalVar> intervals)
    {
        NoOverlapConstraintProto no_overlap = new NoOverlapConstraintProto();
        no_overlap.Intervals.TrySetCapacity(intervals);
        foreach (IntervalVar var in intervals)
        {
            no_overlap.Intervals.Add(var.GetIndex());
        }
 
        Constraint ct = new Constraint(model_);
        ct.Proto.NoOverlap = no_overlap;
        return ct;
    }
 
    public NoOverlap2dConstraint AddNoOverlap2D()
    {
        NoOverlap2dConstraint ct = new NoOverlap2dConstraint(model_);
        ct.Proto.NoOverlap2D = new NoOverlap2DConstraintProto();
        return ct;
    }
 
    public CumulativeConstraint AddCumulative<C>(C capacity)
    {
        CumulativeConstraintProto cumul = new CumulativeConstraintProto();
        LinearExpr capacityExpr = GetLinearExpr(capacity);
        cumul.Capacity = GetLinearExpressionProto(capacityExpr);
 
        CumulativeConstraint ct = new CumulativeConstraint(this, model_);
        ct.Proto.Cumulative = cumul;
        return ct;
    }
 
    // Objective.
 
    public void Minimize(LinearExpr obj)
    {
        SetObjective(obj, true);
    }
 
    public void Maximize(LinearExpr obj)
    {
        SetObjective(obj, false);
    }
 
    void ClearObjective()
    {
        model_.Objective = null;
    }
 
    bool HasObjective()
    {
        return model_.Objective is not null || model_.FloatingPointObjective is not null;
    }
 
    // Search Decision.
 
    public void AddDecisionStrategy(IEnumerable<IntVar> vars,
                                    DecisionStrategyProto.Types.VariableSelectionStrategy var_str,
                                    DecisionStrategyProto.Types.DomainReductionStrategy dom_str)
    {
        DecisionStrategyProto ds = new DecisionStrategyProto();
        ds.Variables.TrySetCapacity(vars);
        foreach (IntVar var in vars)
        {
            ds.Variables.Add(var.Index);
        }
        ds.VariableSelectionStrategy = var_str;
        ds.DomainReductionStrategy = dom_str;
        model_.SearchStrategy.Add(ds);
    }
 
    public void AddHint(IntVar var, long value)
    {
        model_.SolutionHint ??= new PartialVariableAssignment();
        model_.SolutionHint.Vars.Add(var.GetIndex());
        model_.SolutionHint.Values.Add(value);
    }
 
    public void ClearHints()
    {
        model_.SolutionHint = null;
    }
 
    public void AddAssumption(ILiteral lit)
    {
        model_.Assumptions.Add(lit.GetIndex());
    }
 
    public void AddAssumptions(IEnumerable<ILiteral> literals)
    {
        foreach (ILiteral lit in literals)
        {
            AddAssumption(lit);
        }
    }
 
    public void ClearAssumptions()
    {
        model_.Assumptions.Clear();
    }
 
    // Internal methods.
 
    void SetObjective(LinearExpr obj, bool minimize)
    {
        CpObjectiveProto objective = new CpObjectiveProto();
        if (obj is null)
        {
            objective.Offset = 0L;
            objective.ScalingFactor = minimize ? 1L : -1;
        }
        else if (obj is IntVar intVar)
        {
            objective.Offset = 0L;
            objective.Vars.Capacity = 1;
            objective.Vars.Add(intVar.Index);
 
            objective.Coeffs.Capacity = 1;
            if (minimize)
            {
                objective.Coeffs.Add(1L);
                objective.ScalingFactor = 1L;
            }
            else
            {
                objective.Coeffs.Add(-1L);
                objective.ScalingFactor = -1L;
            }
        }
        else
        {
            var dict = var_value_map_;
            dict.Clear();
            long constant = LinearExpr.GetVarValueMap(obj, dict, terms_);
            var dictCount = dict.Count;
            objective.Vars.Capacity = dictCount;
            objective.Vars.AddRange(dict.Keys);
            objective.Coeffs.Capacity = dictCount;
            if (minimize)
            {
                objective.Coeffs.AddRange(dict.Values);
                objective.ScalingFactor = 1L;
                objective.Offset = constant;
            }
            else
            {
                foreach (var coeff in dict.Values)
                {
                    objective.Coeffs.Add(-coeff);
                }
                objective.ScalingFactor = -1L;
                objective.Offset = -constant;
            }
        }
        model_.Objective = objective;
    }
 
    public String ModelStats()
    {
        return CpSatHelper.ModelStats(model_);
    }
 
    public Boolean ExportToFile(String file)
    {
        return CpSatHelper.WriteModelToFile(model_, file);
    }
 
    public String Validate()
    {
        return CpSatHelper.ValidateModel(model_);
    }
 
    private int ConvertConstant(long value)
    {
        if (constant_map_.TryGetValue(value, out var index))
        {
            return index;
        }
 
        index = model_.Variables.Count;
        IntegerVariableProto var = new IntegerVariableProto();
        var.Domain.Capacity = 2;
        var.Domain.Add(value);
        var.Domain.Add(value);
        constant_map_.Add(value, index);
        model_.Variables.Add(var);
        return index;
    }
 
    internal LinearExpr GetLinearExpr<X>(X x)
    {
        if (typeof(X) == typeof(IntVar))
        {
            return (IntVar)(Object)x;
        }
        if (typeof(X) == typeof(long) || typeof(X) == typeof(int) || typeof(X) == typeof(short))
        {
            return LinearExpr.Constant(Convert.ToInt64(x));
        }
        if (typeof(X) == typeof(LinearExpr))
        {
            return (LinearExpr)(Object)x;
        }
        throw new ArgumentException("Cannot convert argument to LinearExpr");
    }
 
    internal LinearExpressionProto GetLinearExpressionProto(LinearExpr expr, bool negate = false)
    {
        var dict = var_value_map_;
        dict.Clear();
        long constant = LinearExpr.GetVarValueMap(expr, dict, terms_);
 
        LinearExpressionProto linear = new LinearExpressionProto();
        var dictCount = dict.Count;
        linear.Vars.Capacity = dictCount;
        linear.Vars.AddRange(dict.Keys);
        linear.Coeffs.Capacity = dictCount;
        if (negate)
        {
            foreach (var coeff in dict.Values)
            {
                linear.Coeffs.Add(-coeff);
            }
            linear.Offset = -constant;
        }
        else
        {
            linear.Coeffs.AddRange(dict.Values);
            linear.Offset = constant;
        }
 
        return linear;
    }
 
    private CpModelProto model_;
    private Dictionary<long, int> constant_map_;
    private Dictionary<int, long> var_value_map_;
    private BoolVar true_literal_;
    private Queue<Term> terms_;
}
 
} // namespace Google.OrTools.Sat