/**
 * Definition for singly-linked list with a random pointer.
 * class ListNode {
 *     int val;
 *     ListNode next, random;
 *     ListNode(int x) { this.val = x; }
 * };
 */
class Solution {
    public ListNode copyRandomList(ListNode head) {
        if (head == null) {
            return null;
        }

        //后部插入新节点
        ListNode cur = head;
        while(cur  != null) {
            ListNode listNode = new ListNode(cur.val);
            listNode.next = cur.next;
            cur.next = listNode;
            cur = listNode.next;
        }

        // 建立random链接
        cur = head;
        while(cur != null) {
            ListNode clone = cur.next;
            if (cur.random != null) {
                clone.random = cur.random.next;
            }
            cur = clone.next;
        }
        //拆分
        cur = head;
        ListNode cloneHead = head.next;
        while(cur.next != null) {
           ListNode next = cur.next;
           cur.next = next.next;
           cur = next;
        }
        return cloneHead;

    }
}