public static ExpressionHolder convertToDNF(ExpressionHolder expHolder)
{
OrExpression dnf = new OrExpression();
var exp = expHolder.getExpression();
var terms = expHolder.getTerms().Values;
for (int i = 0; i < Math.Pow(2, terms.Count); i++)
{
for (int j = 0; j < terms.Count; j++)
{
terms.ElementAt(j).setValue((i & (1 << j)) != 0);
}
if (exp.evaluate())
{
AndExpression and = new AndExpression();
for (int j = 0; j < terms.Count; j++)
{
if ((i & (1 << j)) != 0)
{
and.addExpression(terms.ElementAt(j));
}
else
{
and.addExpression(new Not(terms.ElementAt(j)));
}
}
dnf.addExpression(and);
}
}
return(new ExpressionHolder(dnf, expHolder.getTerms()));
}
public bool getIsDnf()
{
foreach (var exp in this.exps)
{
if (!(exp is AndExpression))
{
return(false);
}
AndExpression and = exp as AndExpression;
foreach (var and_child in and.getExpressions())
{
if (and_child is Term)
{
continue;
}
if (!(and_child is Not))
{
return(false);
}
var not = and_child as Not;
if (!(not.getExpression() is Term))
{
return(false);
}
}
}
return(true);
}
/// <summary>
/// This builds the expression
/// </summary>
/// <returns></returns>
public ExpressionHolder buildExpression(List <IToken> infix_tokens)
{
Parser parser = new Parser();
List <IToken> postfix_Tokens = parser.convertInfixToPostfix(infix_tokens);
Stack <IBooleanExpression> stack = new Stack <IBooleanExpression>();
Dictionary <String, Term> terms = new Dictionary <string, Term>();
foreach (var token in postfix_Tokens)
{
if (token is Word)
{
Word word = token as Word;
if (terms.ContainsKey(word.getWord()) == false)
{
terms[word.getWord()] = new Term(word.getWord(), false);
}
Term term = terms[word.getWord()];
stack.Push(term);
continue;
}
Operation operation = (Operation)token;
char symbol = operation.getSymbol();
if (symbol == Parser.AND || symbol == Parser.OR)
{
try
{
IBooleanExpression left = stack.Pop();
IBooleanExpression right = stack.Pop();
IBooleanExpression result = null;
if (symbol == Parser.AND)
{
result = new AndExpression(left, right);
}
else
{
result = new OrExpression(left, right);
}
stack.Push(result);
continue;
}
catch
{
throw new Exception("Parsing error.");
}
}
else if (symbol == Parser.NOT)
{
try
{
IBooleanExpression right = stack.Pop();
IBooleanExpression result = new Not(right);
stack.Push(result);
continue;
}
catch
{
throw new Exception("Parsing error.");
}
}
else
{
throw new Exception("Unexpected operation was found [ " + symbol + " ]");
}
}
if (stack.Count != 1)
{
throw new Exception("Parsing error : stack does not has one and only one element left, it has " + stack.Count + " element(s)");
}
IBooleanExpression exp = stack.Pop();
return(new ExpressionHolder(exp, terms));
}
