Model.jaba

package signpost;

import java.util.ArrayList;
import java.util.BitSet;
import java.util.Formatter;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Arrays;

import static signpost.Place.*;
import static signpost.Utils.*;

/** The state of a Signpost puzzle.  Each cell has coordinates (x, y),
 *  where 0 <= x < width(),  0 <= y < height().  The upper-left corner of
 *  the puzzle has coordinates (0, height() - 1), and the lower-right corner
 *  is at (width() - 1, 0).
 *
 *  A constructor initializes the squares according to a particular
 *  solution.  A solution is an assignment of sequence numbers from 1 to
 *  size() == width() * height() to square positions so that squares with
 *  adjacent numbers are separated by queen moves. A queen move is a move from
 *  one square to another horizontally, vertically, or diagonally. The effect
 *  is to give each square whose number in the solution is less than
 *  size() an <i>arrow direction</i>, 1 <= d <= 8, indicating the direction
 *  of the next higher numbered square in the solution: d * 45 degrees clockwise
 *  from straight up (i.e., toward higher y coordinates).  The highest-numbered
 *  square has direction 0.  Certain squares can have their values fixed to
 *  those in the solution. Initially, the only two squares with fixed values
 *  are those with the lowest and highest sequence numbers in the solution.
 *
 *  At any given time after initialization, a square whose value is not fixed
 *  may have an unknown value, represented as 0, or a tentative number (not
 *  necessarily that of the solution) between 1 and size(). Squares may be
 *  connected together, indicating that their sequence numbers (unknown or not)
 *  are consecutive.
 *
 *  When square S0 is connected to S1, we say that S1 is the <i>successor</i> of
 *  S0, and S0 is the <i>predecessor</i> of S1.  Sequences of connected squares
 *  with unknown (0) values form a <i>group</i>, identified by a unique
 *  <i>group number</i>.  Numbered cells (whether linked or not) are in group 0.
 *  Unnumbered, unlinked cells are in group -1.
 *
 *  Squares are represented as objects of the inner class Sq (Model.Sq).  A
 *  Model object is itself iterable, yielding its squares in unspecified order.
 *
 *  The puzzle is solved when all cells are contained in a single sequence
 *  of consecutively numbered cells (therefore all in group 0) and all cells
 *  with fixed sequence numbers appear at the corresponding position
 *  in that sequence.
 *
 *  @author
 */
class Model implements Iterable<Model.Sq> {

    /** A Model whose solution is SOLUTION, initialized to its starting,
     *  unsolved state (where only cells with fixed numbers currently
     *  have sequence numbers and no unnumbered cells are connected).
     *  SOLUTION must be a proper solution:
     *      1. It must have dimensions w x h such that w * h >= 2.
     *      2. There must be a sequence of chess-queen moves such that
     *         the sequence of values in the cells reached is 1, 2, ... w * h.
     *  The contents of SOLUTION are copied into this Model, so that subsequent
     *  changes to it have no effect on the Model.
     */
    Model(int[][] solution) {
        if (solution.length == 0 || solution.length * solution[0].length < 2) {
            throw badArgs("must have at least 2 squares");
        }
        _width = solution.length; _height = solution[0].length;
        int last = _width * _height;
        BitSet allNums = new BitSet();

        _allSuccessors = Place.successorCells(_width, _height);
        _solution = new int[_width][_height];
        deepCopy(solution, _solution);

        // DUMMY SETUP
        // FIXME: Remove everything down "// END DUMMY SETUP".

        // END DUMMY SETUP


        // FIXME: Initialize _board so that _board[x][y] contains the Sq object
        //        representing the contents at cell (x, y), _allSquares
        //        contains the list of all Sq objects on the board, and
        //        _solnNumToPlace[k] contains the Place in _solution that
        //        contains sequence number k.  Check that all numbers from
        //        1 - last appear; else throw IllegalArgumentException (see
        //        badArgs utility).

        _solnNumToPlace = new Place[_width*_height+1];
        int check = 1;

        for (int k=1; k < _solnNumToPlace.length; k++){

            for (int i=0; i < _width; i++) {

                for (int j = 0; j < _height; j++) {

                    if (_solution[i][j] == k){

                        _solnNumToPlace[k] = pl(i,j);
                        check++;
                    }
                }
            }
        }

        if ( _solnNumToPlace.length != check){

            throw badArgs("must contain all numbers");
        }



         _board = new Sq[_width][_height];

         for (int i=0; i < _width; i++){
             for (int j=0; j < _height; j++){

                 if (_solnNumToPlace[1].equals(pl(i,j)) || _solnNumToPlace[_solnNumToPlace.length-1].equals(pl(i,j)) ){
                     _board[i][j] = new Sq(i,j,_solution[i][j],true, arrowDirection(i,j),0);
                 }
                 else{
                     _board[i][j] = new Sq(i,j,0,false, arrowDirection(i,j),-1);
                 }

             }
         }

        for (int i=0; i < _width; i++){
            for (int j=0; j < _height; j++){

                _allSquares.add(_board[i][j]);
            }
        }



        // FIXME: For each Sq object on the board, set its _successors and
        //        _predecessor lists to the lists of locations of all cells
        //        that it might connect to (i.e., all cells that are a queen
        //        move away in the direction of its arrow, and of all cells
        //        that might connect to it.

        for(Sq each: _allSquares){



            each._successors = allSuccessors(each.x, each.y, each._dir);


            //each._predecessors = allSuccessors(each.x, each.y, -each._dir);
        }

        _unconnected = last - 1;
    }

    /** Initializes a copy of MODEL. */
    Model(Model model) {
        _width = model.width(); _height = model.height();
        _unconnected = model._unconnected;
        _solnNumToPlace = model._solnNumToPlace;
        _solution = model._solution;
        _usedGroups.addAll(model._usedGroups);
        _allSuccessors = model._allSuccessors;

        // FIXME: Initialize _board and _allSquares to contain copies of the
        //        the Sq objects in MODEL other than their _successor,
        //        _predecessor, and _head fields (which can't necessarily be
        //        set until all the necessary Sq objects are first created.)


        _board = new Sq[_width][_height];

        for (int i=0; i < _width; i++){
            for (int j=0; j < _height; j++){

                _board[i][j] = model._board[i][j];

            }
        }


        for (int i=0; i < _width; i++){
            for (int j=0; j < _height; j++){

                _allSquares.add(_board[i][j]);
            }
        }



        // FIXME: Fill in the _successor, _predecessor, and _head fields of the
        //        copied Sq objects.
    }

    /** Returns the width (number of columns of cells) of the board. */
    final int width() {
        return _width;
    }

    /** Returns the height (number of rows of cells) of the board. */
    final int height() {
        return _height;
    }

    /** Returns the number of cells (and thus, the sequence number of the
     *  final cell). */
    final int size() {
        return _width * _height;
    }

    /** Returns true iff (X, Y) is a valid cell location. */
    final boolean isCell(int x, int y) {
        return 0 <= x && x < width() && 0 <= y && y < height();
    }

    /** Returns true iff P is a valid cell location. */
    final boolean isCell(Place p) {
        return isCell(p.x, p.y);
    }

    /** Returns all cell locations that are a queen move from (X, Y)
     *  in direction DIR, or all queen moves in any direction if DIR = 0. */
    final PlaceList allSuccessors(int x, int y, int dir) {
        return _allSuccessors[x][y][dir];
    }

    /** Returns all cell locations that are a queen move from P in direction
     *  DIR, or all queen moves in any direction if DIR = 0. */
    final PlaceList allSuccessors(Place p, int dir) {
        return _allSuccessors[p.x][p.y][dir];
    }

    /** Initialize MODEL to an empty WIDTH x HEIGHT board with a null solution.
     */
    void init(int width, int height) {
        if (width <= 0 || width * height < 2) {
            throw badArgs("must have at least 2 squares");
        }
        _width = width; _height = height;
        _unconnected = _width * _height - 1;
        _solution = null;
        _usedGroups.clear();
        // FIXME: Initialize _board to contain nulls and clear all objects from
        //        _allSquares.

        _board = new Sq[_width][_height];

        _allSquares = new ArrayList<Sq>();


        // FIXME: Initialize _allSuccSquares so that _allSuccSquares[x][y][dir]
        //        is a list of all the Places on the board that are a queen
        //        move in direction DIR from (x, y) and _allSuccSquares[x][y][0]
        //        is a list of all Places that are one queen move from in
        //        direction from (x, y).

        _allSuccessors = successorCells(_width, _height);
    }

    /** Remove all connections and non-fixed sequence numbers. */
    void restart() {
        for (Sq sq : this) {
            sq.disconnect();
        }
        assert _unconnected == _width * _height - 1;
    }

    /** Return the number array that solves the current puzzle (the argument
     *  the constructor.  The result must not be subsequently modified.  */
    final int[][] solution() {
        return _solution;
    }

    /** Return the position of the cell with sequence number N in my
     *  solution. */
    Place solnNumToPlace(int n) {
        return _solnNumToPlace[n];
    }

    /** Return the current number of unconnected cells. */
    final int unconnected() {
        return _unconnected;
    }

    /** Returns true iff the puzzle is solved. */
    final boolean solved() {
        return _unconnected == 0;
    }

    /** Return the cell at (X, Y). */
    final Sq get(int x, int y) {
        return _board[x][y];
    }

    /** Return the cell at P. */
    final Sq get(Place p) {
        return p == null ? null : _board[p.x][p.y];
    }

    /** Return the cell at the same position as SQ (generally from another
     *  board), or null if SQ is null. */
    final Sq get(Sq sq) {
        return sq == null ? null : _board[sq.x][sq.y];
    }

    /** Connect all numbered cells with successive numbers that as yet are
     *  unconnected and are separated by a queen move.  Returns true iff
     *  any changes were made. */
    boolean autoconnect() {

        for (int x = 0; x < _width; x++) {
            for (int y = 0; y < _height; y++) {
                Sq mySquare = _board[x][y];
                if (mySquare._successor == null && mySquare._sequenceNum != 0) {
                    for (Place temp : allSuccessors(x, y, _board[x][y]._dir)) {
                        Sq potentialSuccessor = get(temp);
                        if (potentialSuccessor._sequenceNum == mySquare._sequenceNum + 1)          {
                            if (mySquare.connectable(potentialSuccessor)) {
                                mySquare.connect(potentialSuccessor);
                                return true;
                            }
                        }
                    }
                }
            }
        }
        return false; // FIXME
    }

    /** Sets the numbers in my squares to the solution from which I was
     *  last initialized by the constructor. */
    void solve() {
        // FIXME

       // _board = new Sq[_width][_height];

        for (int i=0; i < _width; i++){
            for (int j=0; j < _height; j++){

                if (_board[i][j]._hasFixedNum == false ){
                    _board[i][j] = new Sq(i,j,_solution[i][j],false, arrowDirection(i,j),-1);
                }

            }
        }

        _unconnected = 0;
    }

    /** Return the direction from cell (X, Y) in the solution to its
     *  successor, or 0 if it has none. */
    private int arrowDirection(int x, int y) {
        int seq0 = _solution[x][y];


        if (seq0 < _solnNumToPlace.length-1 ){

            if (_solnNumToPlace[seq0+1] != null){

                return _solnNumToPlace[seq0].dirOf(_solnNumToPlace[seq0+1]);
            }
        }

        return 0;
    }

    /** Return a new, currently unused group number > 0.  Selects the
     *  lowest not currently in used. */
    private int newGroup() {
        for (int i = 1; true; i += 1) {
            if (_usedGroups.add(i)) {
                return i;
            }
        }
    }

    /** Indicate that group number GROUP is no longer in use. */
    private void releaseGroup(int group) {
        _usedGroups.remove(group);
    }

    /** Combine the groups G1 and G2, returning the resulting group. Assumes
     *  G1 != 0 != G2 and G1 != G2. */
    private int joinGroups(int g1, int g2) {
        assert (g1 != 0 && g2 != 0);
        if (g1 == -1 && g2 == -1) {
            return newGroup();
        } else if (g1 == -1) {
            return g2;
        } else if (g2 == -1) {
            return g1;
        } else if (g1 < g2) {
            releaseGroup(g2);
            return g1;
        } else {
            releaseGroup(g1);
            return g2;
        }
    }

    @Override
    public Iterator<Sq> iterator() {
        return _allSquares.iterator();
    }

    @Override
    public String toString() {
        String hline;
        hline = "+";
        for (int x = 0; x < _width; x += 1) {
            hline += "------+";
        }

        Formatter out = new Formatter();
        for (int y = _height - 1; y >= 0; y -= 1) {
            out.format("%s%n", hline);
            out.format("|");
            for (int x = 0; x < _width; x += 1) {
                Sq sq = get(x, y);
                if (sq.hasFixedNum()) {
                    out.format("+%-5s|", sq.seqText());
                } else {
                    out.format("%-6s|", sq.seqText());
                }
            }
            out.format("%n|");
            for (int x = 0; x < _width; x += 1) {
                Sq sq = get(x, y);
                if (sq.predecessor() == null && sq.sequenceNum() != 1) {
                    out.format(".");
                } else {
                    out.format(" ");
                }
                if (sq.successor() == null
                    && sq.sequenceNum() != size()) {
                    out.format("o ");
                } else {
                    out.format("  ");
                }
                out.format("%s |", ARROWS[sq.direction()]);
            }
            out.format("%n");
        }
        out.format(hline);
        return out.toString();
    }

    @Override
    public boolean equals(Object obj) {
        Model model = (Model) obj;
        return (_unconnected == model._unconnected
                && _width == model._width && _height == model._height
                && Arrays.deepEquals(_solution, model._solution)
                && Arrays.deepEquals(_board, model._board));
    }

    @Override
    public int hashCode() {
        return Arrays.deepHashCode(_solution) * Arrays.deepHashCode(_board);
    }

    /** Represents a square on the board. */
    final class Sq {
        /** A square at (X0, Y0) with arrow in direction DIR (0 if not
         *  set), group number GROUP, sequence number SEQUENCENUM (0
         *  if none initially assigned), which is fixed iff FIXED. */
        Sq(int x0, int y0, int sequenceNum, boolean fixed, int dir, int group) {
            x = x0; y = y0;
            pl = pl(x, y);
            _hasFixedNum = fixed;
            _sequenceNum = sequenceNum;
            _dir = dir;
            _head = this;
            _group = group;
        }

        /** A copy of OTHER, excluding head, successor, and predecessor. */
        Sq(Sq other) {
            this(other.x, other.y, other._sequenceNum, other._hasFixedNum,
                 other._dir, other._group);
            _successor = _predecessor = null;
            _head = this;
            _successors = other._successors;
            _predecessors = other._predecessors;
        }

        /** Return my current sequence number, or 0 if none assigned. */
        int sequenceNum() {
            return _sequenceNum;
        }

        /** Fix my current sequence number at N>0.  It is an error if my number
         *  is not initially 0 or N. */
        void setFixedNum(int n) {
            if (n == 0 || (_sequenceNum != 0 && _sequenceNum != n)) {
                throw badArgs("sequence number may not be fixed");
            }
            _hasFixedNum = true;
            if (_sequenceNum == n) {
                return;
            } else {
                releaseGroup(_head._group);
            }
            _sequenceNum = n;
            for (Sq sq = this; sq._successor != null; sq = sq._successor) {
                sq._successor._sequenceNum = sq._sequenceNum + 1;
            }
            for (Sq sq = this; sq._predecessor != null; sq = sq._predecessor) {
                sq._predecessor._sequenceNum = sq._sequenceNum - 1;
            }
        }

        /** Unfix my sequence number if it is currently fixed; otherwise do
         *  nothing. */
        void unfixNum() {
            Sq next = _successor, pred = _predecessor;
            _hasFixedNum = false;
            disconnect();
            if (pred != null) {
                pred.disconnect();
            }
            _sequenceNum = 0;
            if (next != null) {
                connect(next);
            }
            if (pred != null) {
                pred.connect(this);
            }
        }

        /** Return true iff my sequence number is fixed. */
        boolean hasFixedNum() {
            return _hasFixedNum;
        }

        /** Returns direction of my arrow (0 if no arrow). */
        int direction() {
            return _dir;
        }

        /** Return my current predecessor. */
        Sq predecessor() {
            return _predecessor;
        }

        /** Return my current successor. */
        Sq successor() {
            return _successor;
        }

        /** Return the head of the connected sequence I am currently in. */
        Sq head() {
            return _head;
        }

        /** Return the group number of my group.  It is 0 if I am numbered, and
         *  -1 if I am alone in my group. */
        int group() {
            if (_sequenceNum != 0) {
                return 0;
            } else {
                return _head._group;
            }
        }

        /** Size of alphabet. */
        static final int ALPHA_SIZE = 26;

        /** Return a textual representation of my sequence number or
         *  group/position. */
        String seqText() {
            if (_sequenceNum != 0) {
                return String.format("%d", _sequenceNum);
            }
            int g = group() - 1;
            if (g < 0) {
                return "";
            }

            String groupName =
                String.format("%s%s",
                              g < ALPHA_SIZE ? ""
                              : Character.toString((char) (g / ALPHA_SIZE
                                                           + 'a')),
                              Character.toString((char) (g % ALPHA_SIZE
                                                         + 'a')));
            if (this == _head) {
                return groupName;
            }
            int n;
            n = 0;
            for (Sq p = this; p != _head; p = p._predecessor) {
                n += 1;
            }
            return String.format("%s%+d", groupName, n);
        }

        /** Return locations of my potential successors. */
        PlaceList successors() {
            return _successors;
        }

        /** Return locations of my potential predecessors. */
        PlaceList predecessors() {
            return _predecessors;
        }

        /** Returns true iff I may be connected to cell S1, that is:
         *  + S1 is in the correct direction from me.
         *  + S1 does not have a current predecessor, and I do not have a
         *    current successor.
         *  + If S1 and I both have sequence numbers, then mine is
         *    sequenceNum() == S1.sequenceNum() - 1.
         *  + If neither S1 nor I have sequence numbers, then we are not part
         *    of the same connected sequence.
         */
        boolean connectable(Sq s1) {

            if (_successors.contains(s1.pl) && s1._predecessor == null && _successor == null ){

               if (sequenceNum() != 0 && s1.sequenceNum() != 0 && (sequenceNum() == s1.sequenceNum()-1 )){
                   return true;
               }
               else if (sequenceNum() == 0 && s1.sequenceNum() == 0 && ( _head != s1._head)){
                   return true;
               }
               else{}


            }
            return false;
        }

        /** Connect me to S1, if we are connectable; otherwise do nothing.
         *  Returns true iff we were connectable.  Assumes S1 is in the proper
         *  arrow direction from me. */
        boolean connect(Sq s1) {
            if (!connectable(s1)) {
                return false;
            }
            int sgroup = s1.group();

            _unconnected -= 1;

            // FIXME: Connect me to my successor:
            //        + Set my _successor field and S1's _predecessor field.
            //        + If I have a number, number all my successors
            //          accordingly (if needed).
            //        + If S1 is numbered, number me and my predecessors
            //          accordingly (if needed).
            //        + Set the _head fields of my successors to my _head.
            //        + If either of this or S1 used to be unnumbered and is
            //          now numbered, release its group of whichever was
            //          unnumbered, so that it can be reused.
            //        + If both this and S1 are unnumbered, set the group of
            //          my head to the result of joining the two groups.
            boolean thisWasNumbered, s1WasNumbered;
            thisWasNumbered = s1WasNumbered = false;
            this._successor = s1; s1._predecessor = this;
            if (this._sequenceNum != 0) { // Condition 2: I had a #
                if (s1._sequenceNum == 0)
                    s1WasNumbered = true;
                Sq successorPtr = this._successor;
                int offset = this._sequenceNum;
                while (successorPtr != null) {
                    offset += 1;
                    successorPtr._sequenceNum = offset;
                    successorPtr = successorPtr._successor;
                }
            }
            if (s1._sequenceNum != 0) { // Condition 3: S1 had a #
                if (this._sequenceNum == 0)
                    thisWasNumbered = true;
                this._sequenceNum = s1._sequenceNum - 1;
                Sq predecessorPtr = this._predecessor;
                int initNum = this._sequenceNum;
                while (predecessorPtr != null) {
                    initNum -= 1;
                    predecessorPtr._sequenceNum = initNum;
                    predecessorPtr = predecessorPtr._predecessor;
                }
            }
            // Condition 4 : Head of my successors is my head
            Sq successorPtr = this._successor;
            while (successorPtr != null) {
                successorPtr._head = this._head;
                successorPtr = successorPtr._successor;
            }
            // Condition 5: Either was numbered
            if (thisWasNumbered || s1WasNumbered) {
                if (thisWasNumbered) {
                    releaseGroup(this._group);
                }
                else if (s1WasNumbered) {
                    releaseGroup(s1._group);
                }
            }
            // Condition 6: Both are unnumbered
            if ((this._sequenceNum == 0) && (s1._sequenceNum == 0))  {
                this._head._group = joinGroups(this._head._group, s1._head._group);
            }

            return true;
        }

        /** Disconnect me from my current successor, if any. */
        void disconnect() {
            Sq next = _successor;
            if (next == null) {
                return;
            }
            _unconnected += 1;
            next._predecessor = _successor = null;
            if (_sequenceNum == 0) {
                // FIXME: If both this and next are now one-element groups,
                //        release their former group and set both group
                //        numbers to -1.
                //        Otherwise, if either is now a one-element group, set
                //        its group number to -1 without releasing the group
                //        number.
                //        Otherwise, the group has been split into two multi-
                //        element groups.  Create a new group for next.
            } else {
                // FIXME: If neither this nor any square in its group that
                //        precedes it has a fixed sequence number, set all
                //        their sequence numbers to 0 and create a new group
                //        for them if this has a current predecessor (other
                //        set group to -1).
                // FIXME: If neither next nor any square in its group that
                //        follows it has a fixed sequence number, set all
                //        their sequence numbers to 0 and create a new
                //        group for them if next has a current successor
                //        (otherwise set next's group to -1.)
            }
            // FIXME: Set the _head of next and all squares in its group to
            //        next.
        }

        @Override
        public boolean equals(Object obj) {
            Sq sq = (Sq) obj;
            return sq != null
                && pl == sq.pl
                && _hasFixedNum == sq._hasFixedNum
                && _sequenceNum == sq._sequenceNum
                && _dir == sq._dir
                && (_predecessor == null) == (sq._predecessor == null)
                && (_predecessor == null
                    || _predecessor.pl == sq._predecessor.pl)
                && (_successor == null || _successor.pl == sq._successor.pl);
        }

        @Override
        public int hashCode() {
            return (x + 1) * (y + 1) * (_dir + 1)
                * (_hasFixedNum ? 3 : 1) * (_sequenceNum + 1);
        }

        /** The coordinates of this square in the board. */
        protected final int x, y;
        /** My coordinates as a Place. */
        protected final Place pl;
        /** The first in the currently connected sequence of cells ("group")
         *  that includes this one. */
        private Sq _head;
        /** If _head == this, then the group number of the group of which this
         *  is a member.  Numbered sequences have a group number of 0,
         *  regardless of the value of _group. Unnumbered one-member groups
         *  have a group number of -1.   */
        private int _group;
        /** True iff assigned a fixed sequence number. */
        private boolean _hasFixedNum;
        /** The current imputed or fixed sequence number,
         *  numbering from 1, or 0 if there currently is none. */
        private int _sequenceNum;
        /** The arrow direction. The possible values are 0 (for unset),
         *  1 for northeast, 2 for east, 3 for southeast, 4 for south,
         *  5 for southwest, 6 for west, 7 for northwest, and 8 for north. */
        private int _dir;
        /** The current predecessor of this square, or null if there is
         *  currently no predecessor. */
        private Sq _predecessor;
        /** The current successor of this square, or null if there is
         *  currently no successor. */
        private Sq _successor;
        /** Locations of my possible predecessors. */
        private PlaceList _predecessors;
        /** Locations of my possible successor. */
        private PlaceList _successors;
    }

    /** ASCII denotations of arrows, indexed by direction. */
    private static final String[] ARROWS = {
        " *", "NE", "E ", "SE", "S ", "SW", "W ", "NW", "N "
    };

    /** Number of squares that haven't been connected. */
    private int _unconnected;
    /** Dimensions of board. */
    private int _width, _height;
    /** Contents of board, indexed by position. */
    private Sq[][] _board;
    /** Contents of board as a sequence of squares for convenient iteration. */
    private ArrayList<Sq> _allSquares = new ArrayList<>();
    /** _allSuccessors[x][y][dir] is a sequence of all queen moves possible
     *  on the board of in direction dir from (x, y).  If dir == 0,
     *  this is all places that are a queen move from (x, y) in any
     *  direction. */
    private PlaceList[][][] _allSuccessors;
    /** The solution from which this Model was built. */
    private int[][] _solution;
    /** Inverse mapping from sequence numbers to board positions. */
    private Place[] _solnNumToPlace;
    /** The set of positive group numbers currently in use. */
    private HashSet<Integer> _usedGroups = new HashSet<>();

}