138

 每个pointer有两个指向，next    random, 

node1, nod

 

output 返回deepcopy,  

 

四步完成

1. 检查当前node 是否被拷贝过，如果没有，先拷贝一份当前node  到hash map;

2. 把 copy node 加入到list 中，即 copy next pointer;

3.copy 当前弄得的random pointer

4. 对于original list 每个节点都做以上三个动作。

 

建立dummy node   这是新建list 的头节点；-不用处理 corner case

 

public class solution
public RandomListNode copy(RandomListNode head){
if(head==null) return null;

// sentinel node to help construct the deep copy

randdomListNode dummy= new RandomListNode(0);
RandomListNode cur=dummy;

//maintain the mapping between the node in the original lsit and the corresponding node in the new list

Map<randomListNode, RandomListNode> map= new HashMap<>();
while(head!=null){

// copy the node if necessay'

if(!map.containsKey(head)){
map.put(head,new RandomLsitNode(head.value));
}
cur.next=map.get(head);
if(head.random!=null){
if(!map.containsKey(head.random)){
map.put(head.random,new RandomListNode(head.random.value);

//connect the copied node to the deep copy list;

}
cur.next.random=map.get(head.random);

//  copy the random node if necesay

}
head=head.next;
cur=cur.next;
}
return dummy.next;
}}