private static class CellKey {
private final int _row;
private final int _col;
private final int _hash;
private int _hash = -1;
protected CellKey(int row, int col) {
_row = row;
_col = col;
_hash = (17 * 37 + row) * 37 + col;
}
@Override
public int hashCode() {
if( _hash == -1 ) _hash = (17 * 37 + _row) * 37 + _col;
return _hash;