public static void main(String args[]) throws IOException {
// Main array where we will store our initial clauses.
ArrayList<Clause> Clauses = new ArrayList<Clause>();
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
// Creating data structure.
System.out.println("How many clauses does your formula in the Conjuctive Normal Form have?");
int nClauses = Integer.parseInt(in.readLine());
System.out.println("Please introduce your clauses.");
System.out.println("(Input description in the readme file.");
for (int i = 0; i < nClauses; i++) {
String literalsList = in.readLine();
String[] literals = literalsList.split(" ");
Clause clause = new Clause();
for (int i1 = 0; i1 < literals.length; i1++) {
clause.addLiteral(literals[i1]);
}
Clauses.add(clause);
}
// End of data structure
if (DLL(Clauses)) {
System.out.println("Result: The formula is satisfactable.");
} else {
System.out.println("Result: The formula is not satisfactable.");
}
}
/* This is the main algorithm.
* It receives a formula and processes it until
* it can return true or false.
*/
static boolean DLL(ArrayList<Clause> Clauses) {
// Unitary Propagation
while (true) {
String literalToRemove = searchSingleLiteral(Clauses);
if (!literalToRemove.equals("NotFoundYet")) {
printClauses(Clauses);
System.out.println("Performing unitary propagation with: " + literalToRemove);
removeClauses(literalToRemove, Clauses);
cutClauses(literalToRemove, Clauses);
printClauses(Clauses);
if (Clauses.size() == 0) {
System.out.println("All clauses removed. Returning true.");
return true;
}
if (hasFalsehood(Clauses)) {
System.out.println("Falsehood detected. Returning false.");
return false;
} else if (hasEmptyClause(Clauses)) {
System.out.println("Empty clause detected. Returning false.");
return false;
}
} else {
System.out.println("No single literals.");
System.out.println("Cannot perform unitary propagation.");
break;
}
}
ArrayList<Clause> copy1 = new ArrayList<Clause>();
ArrayList<Clause> copy2 = new ArrayList<Clause>();
for (Clause c : Clauses) {
Clause c2 = new Clause();
for (String s : c.literals) {
c2.addLiteral(s);
}
copy1.add(c2);
}
for (Clause c : Clauses) {
Clause c2 = new Clause();
for (String s : c.literals) {
c2.addLiteral(s);
}
copy2.add(c2);
}
Clause clause1 = new Clause();
Clause clause2 = new Clause();
String l1 = pickLiteral(Clauses);
String l2 = "";
if (l1.startsWith("-")) l2 = l1.substring(1);
else l2 = "-" + l1;
clause1.addLiteral(l1);
clause2.addLiteral(l2);
copy1.add(clause1);
copy2.add(clause2);
// Moment of the truth
System.out.println("Adding clause: [" + l1 + "]");
if (DLL(copy1) == true) {
return true;
} else {
System.out.println("Trying opposite clause: [" + l2 + "]");
return DLL(copy2);
}
}
