//
// PRIVATE METHODS
//
private bool dpll(List <Sentence> clauses, List <Symbol> symbols, Model model)
{
// List<Sentence> clauseList = asList(clauses);
List <Sentence> clauseList = clauses;
// System.Console.WriteLine("clauses are " + clauses.ToString());
// if all clauses are true return true;
if (areAllClausesTrue(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return(true);
}
// if even one clause is false return false
if (isEvenOneClauseFalse(model, clauseList))
{
// System.Console.WriteLine(model.ToString());
return(false);
}
// System.Console.WriteLine("At least one clause is unknown");
// try to find a unit clause
SymbolValuePair svp = findPureSymbolValuePair(clauseList, model,
symbols);
if (svp.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List <Symbol> newSymbols = new List <Symbol>(copy);
newSymbols.Remove(new Symbol(svp.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp.symbol.getValue()),
svp.value);
return(dpll(clauses, newSymbols, newModel));
}
SymbolValuePair svp2 = findUnitClause(clauseList, model, symbols);
if (svp2.notNull())
{
Symbol[] copy = new Symbol[symbols.Count];
symbols.CopyTo(copy);
List <Symbol> newSymbols = new List <Symbol>(copy);
newSymbols.Remove(new Symbol(svp2.symbol.getValue()));
Model newModel = model.extend(new Symbol(svp2.symbol.getValue()),
svp2.value);
return(dpll(clauses, newSymbols, newModel));
}
Symbol symbol = (Symbol)symbols[0];
// System.Console.WriteLine("default behaviour selecting " + symbol);
Symbol[] symbolsArr = new Symbol[symbols.Count];
symbols.CopyTo(symbolsArr);
List <Symbol> newSymbols2 = symbolsArr.ToList <Symbol>();
newSymbols2.RemoveAt(0);
return(dpll(clauses, newSymbols2, model.extend(symbol, true)) || dpll(
clauses, newSymbols2, model.extend(symbol, false)));
}
private bool Dpll(ISet <Sentence> clauses, IList <Symbol> symbols, Model model)
{
// IList<Sentence> clauseList = asList(clauses);
IList <Sentence> clauseList = clauses.ToList();
// System.out.println("clauses are " + clauses.toString());
// if all clauses are true return true;
if (this.AreAllClausesTrue(model, clauseList))
{
// System.out.println(model.toString());
return(true);
}
// if even one clause is false return false
if (this.IsEvenOneClauseFalse(model, clauseList))
{
// System.out.println(model.toString());
return(false);
}
// System.out.println("At least one clause is unknown");
// try to find a unit clause
SymbolValuePair svp = this.FindPureSymbolValuePair(clauseList, model);
IList <Symbol> newSymbols;
if (svp.NotNull())
{
newSymbols = symbols.ToList();
newSymbols.Remove(new Symbol(svp.Symbol.Value));
Model newModel = model.Extend(new Symbol(svp.Symbol.Value),
svp.Value);
return(Dpll(clauses, newSymbols, newModel));
}
SymbolValuePair svp2 = this.FindUnitClause(clauseList, model);
if (svp2.NotNull())
{
newSymbols = symbols.ToList();
newSymbols.Remove(new Symbol(svp2.Symbol.Value));
Model newModel = model.Extend(new Symbol(svp2.Symbol.Value),
svp2.Value);
return(Dpll(clauses, newSymbols, newModel));
}
Symbol symbol = symbols[0];
// System.out.println("default behaviour selecting " + symbol);
newSymbols = symbols.ToList();
newSymbols.RemoveAt(0);
return(Dpll(clauses, newSymbols, model.Extend(symbol, true)) || Dpll(
clauses, newSymbols, model.Extend(symbol, false)));
}
