private void csp() {
        Integer v = getNextUnvisitedVariable();
        if (v == null)  {
            // No unassigned variables, found a solution
            solutions.add(Arrays.copyOf(assignments, assignments.length));

            for (int i = 0; i < N; i++)
                assert(isAssignmentValid(i, assignments[i]));
        }
        else {
            visitedVariables[v] = true;

            for (int i = 0; i < N; i++) {
                if (isAssignmentValid(v, i)) {
                    board[v][i] = BlockType.Q;
                    assignments[v] = i;
                    List<BoardPosition> conflictedPositions = markConflictedPositions(v, i);
                    boolean shouldContinue = forwardChecking();
                    if (shouldContinue)
                        csp();
                    unmarkConflictedPositions(conflictedPositions);
                    assignments[v] = null;
                    board[v][i] = BlockType.None;
                }
            }

            visitedVariables[v] = false;
        }
    }