bug fix for odd-size tables

diff --git a/nqueens/nqueens.cc b/nqueens/nqueens.cc
index bed871abdc5966baf3fed47bc9f4a8744cb0c492..616600eb5ab4173e966919a3438a38bec29e410a 100644 (file)
--- a/nqueens/nqueens.cc
+++ b/nqueens/nqueens.cc
@@ -211,7 +211,8 @@ void originalNqueensEncoding(int N){
        }
 
        //Symmetry breaking constraint
-       for (int i=0; i<N/2; i++){
+       int mid = 1+ ((N-1)/2);
+       for (int i=0; i<mid; i++){
                vars.push_back(VarName[0][i]);
        }
        Or(vars, cnf);
@@ -442,20 +443,14 @@ void diagonallyDifferentConstraintBothDir(CSolver *solver, int N, vector<Element
 } 
 
 void symmetryBreakingConstraint(CSolver *solver, int N, vector<Element*>& elems){
-       Predicate *eq = solver->createPredicateOperator(SATC_EQUALS);
-       vector<BooleanEdge> constr;
-       for(int i=0; i<N/2; i++){
-               Element *e1x = elems[0];
-               Element *e2x = solver->getElementConst(2, (uint64_t)i);
-               Element *inputs2 [] = {e1x, e2x};
-               BooleanEdge equals = solver->applyPredicate(eq, inputs2, 2);
-               constr.push_back( equals);
-       }
-       solver->addConstraint(solver->applyLogicalOperation(SATC_OR, &constr[0], constr.size()) );
-       
        Predicate *lt = solver->createPredicateOperator(SATC_LT);
+       int mid = N/2 + N%2;
        Element *e1x = elems[0];
-       Element *e2x = elems[N-1];
+       Element *e2x = solver->getElementConst(2, mid);
+       Element *inputs [] = {e1x, e2x};
+       solver->addConstraint(solver->applyPredicate(lt, inputs, 2));
+       
+       e2x = elems[N-1];
        Element *inputs2 [] = {e1x, e2x};
        BooleanEdge equals = solver->applyPredicate(lt, inputs2, 2);
        solver->addConstraint(equals);