复制链表

 

 方法1 ：先拼接 再拆分

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/
class Solution {
     //避免null.next
    public Node copyRandomList(Node head) {
        if(head == null) return null;
        Node cur  =head;
        //7  7 13 13 11 11 10 10 1 1 null
        while(cur!=null){
            Node tmp  = new Node(cur.val);
            tmp.next  =cur.next;
            cur.next   =tmp;
            cur = cur.next.next;
        }
        cur=  head;
        //修改新的链表random
        while(cur!=null){
            if(cur.random!=null){//如果cur.random==null,cur.random.next:NullPointerException
                   cur.next.random =cur.random.next;
            }
            cur =cur.next.next;
        }
        cur =head;
        Node last =head.next,so=head.next;
        //         while(xx!=null){
        //     x.next  =x.next.next;
          
        //     xx.next = xx.next.next;//xx.next已经是null,NullPointerException
            
        //     x =x.next;
        //     xx = xx.next;
        // }
          while(last.next!=null){
            cur.next  =cur.next.next; 
            last.next = last.next.next;
            cur =cur.next;
            last = last.next;
        }
            cur.next = null;//xx.next已经是null,两条链表最后都是null
            return so;//last已经是新链表的最后面，所以要返回so
    }
}

方法2 Map 先存下来，再遍历修改next 和random

让每个单独的节点形成链表

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/
class Solution {
    HashMap<Node,Node> map  = new HashMap();
    public Node copyRandomList(Node head) {
        if(head == null) return null;
       Node cur = head;
       while(cur!=null){
           Node tmp = new Node(cur.val);
           map.put(cur,tmp);
           cur = cur.next;
       }
       cur = head;
         while(cur!=null){
           map.get(cur).next = map.get(cur.next);
            map.get(cur).random = map.get(cur.random);
           cur = cur.next;
       }
       return map.get(head);
}
}