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

    public RandomListNode copyRandomList(RandomListNode head) {
        if (head == null) return null;
        Map<RandomListNode, RandomListNode> map = new HashMap<>();
        RandomListNode node = head;
        while (node != null) {
            map.put(node, new RandomListNode(node.label));
            node = node.next;
        }
        node = head;
        while (node != null) {
            map.get(node).next = map.get(node.next);
            map.get(node).random = map.get(node.random);
            node = node.next;
        }
        return map.get(head);       
    }