code: public static GeometryIndex getLinearRingIndex(Geometry geometry, Coordinate c) {
  		if (Geometry.LINEAR_RING.equals(geometry.getGeometryType())) {
  			IndexedLinearRing ring = helper.createLinearRing(geometry);
  			if (ring.containsCoordinate(c)) {
  				return ring.getIndex();
  			}
  		} else if (Geometry.POLYGON.equals(geometry.getGeometryType())) {
  			IndexedPolygon polygon = helper.createPolygon(geometry);
  			for (IndexedLinearRing hole : polygon.getHoles()) {
  				if (hole.containsCoordinate(c)) {
  					return hole.getIndex();
  				}
  			}
  			if (polygon.getShell().containsCoordinate(c)) {
  				return polygon.getShell().getIndex();
  			}
  		} else if (Geometry.MULTI_POLYGON.equals(geometry.getGeometryType())) {
  			IndexedMultiPolygon multipolygon = helper.createMultiPolygon(geometry);
  			for (IndexedPolygon polygon : multipolygon.getPolygons()) {
  				for (IndexedLinearRing hole : polygon.getHoles()) {
  					if (hole.containsCoordinate(c)) {
  						return hole.getIndex();
  					}
  				}
  				if (polygon.getShell().containsCoordinate(c)) {
  					return polygon.getShell().getIndex();
  				}
  			}
  		}
  		return null;
  	}
docs: Get the index of the (smallest) linear ring of the geometry that contains this coordinate.
  
  @param geometry
  @param c
  @return the index (empty array indicates no containment)
  @since 1.3.0