import it.unimi.dsi.fastutil.ints.IntSets; //导入依赖的package包/类
public IntMapGraph(Int2ObjectMap<IntSet> map) {
	this.map = map;
	if (map.defaultReturnValue() == null || !map.defaultReturnValue().equals(IntSets.EMPTY_SET)) {
		LOGGER.warn("It is necessary to set default return value of the map as the empty set.");
		map.defaultReturnValue(IntSets.EMPTY_SET);
	}
	
	int maxNodeIndex = 0, numArcs = 0;
	for (Entry<IntSet> x : map.int2ObjectEntrySet()) {
		if (x.getIntKey() > maxNodeIndex)
			maxNodeIndex = x.getIntKey();
		for (int succ : x.getValue()) {
			if (succ > maxNodeIndex)
				maxNodeIndex = succ;
			numArcs++;
		}
	}
	
	this.numArcs  = numArcs;
	this.numNodes = maxNodeIndex+1;
}
 

import it.unimi.dsi.fastutil.ints.IntSets; //导入依赖的package包/类
public IntCollection get(T key) {
    return map.getOrDefault(key, IntSets.EMPTY_SET);
}
 

import it.unimi.dsi.fastutil.ints.IntSets; //导入依赖的package包/类
/**
 * Returns the nodes which are already expanded with the specified node.
 *
 * @param entry the id of the node for which the expansions should be returned
 * @return the nodes which are already expanded with the specified node
 */
public IntSet getExpanded(SpatialEntry entry) {
  IntSet exp = expanded.get(getPageID(entry));
  return (exp != null) ? exp : IntSets.EMPTY_SET;
}