138. Copy List with Random Pointer

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

题目含义：深度拷贝一个列表，列表中的节点包含random成员

思路：以每一个节点为key，构造一个实例作为value维护在map中，然后从head开始依次连接各节点

 1     public RandomListNode copyRandomList(RandomListNode head) {
 2         if (head == null) return null;
 3         Map<RandomListNode, RandomListNode> map = new HashMap<>();
 4         RandomListNode node = head;
 5         while (node != null) {
 6             map.put(node, new RandomListNode(node.label));
 7             node = node.next;
 8         }
 9         node = head;
10         while (node != null) {
11             map.get(node).next = map.get(node.next);
12             map.get(node).random = map.get(node.random);
13             node = node.next;
14         }
15         return map.get(head);       
16     }