1.基础的生成单链表的一个流程。首先生成原始的链表，此阶段只关注.next指针域，并用一个Map记录下对应关系
2.生成.random的指针域，用Map记录的对应关系去指示
public Node copyRandomList(Node head) {
if (head == null) {
return null;
}
Node resNode = new Node(head.val);
Node preNode = resNode;
Node headNode = head;
Node crrNode;
headNode = headNode.next;
HashMap<Node, Node> map = new HashMap<Node, Node>();
map.put(head, resNode);
while (headNode != null) {
int val = headNode.val;
crrNode = new Node(val);
map.put(headNode, crrNode);
preNode.next = crrNode;
headNode = headNode.next;
preNode = crrNode;
}
headNode = head;
crrNode = resNode;
while (headNode != null) {
Node randomNode = map.get(headNode.random);
crrNode.random = randomNode;
crrNode = crrNode.next;
headNode = headNode.next;
}
return resNode;
}