图形
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BFS
class Solution {
public Node cloneGraph ( Node node ) {
if (node == null ) {
return null ;
}
Map< Node> map = new HashMap<> ();
Queue< Node> queue = new LinkedList<> ();
queue . offer(node);
Node newHead = new Node (node . val);
map . put(node, newHead);
while ( ! queue . is
