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.

給定一個連結串列，每個節點包含一個額外增加的隨機指標，該指標可以指向連結串列中的任何節點或空節點。

要求返回這個連結串列的深度拷貝。 

1ms

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 
 3  * class RandomListNode {
 4  *     int label;
 5  *     RandomListNode next, random;
 6  *     RandomListNode(int x) { this.label = x; }
 7  * };
 8  */
 9 public class Solution {
10     public RandomListNode copyRandomList(RandomListNode head) {
11         RandomListNode res = new RandomListNode(0
 
);
12         RandomListNode p = res;
13         RandomListNode curr = head;
14         while (curr != null) {
15             p.next = clone(curr);
16             curr = curr.next;
17             p = p.next;
18         }
19         return res.next;
20     }
21     
22     private RandomListNode clone(RandomListNode node) {
 
23         RandomListNode newNode = new RandomListNode(node.label);
24         if (node.random != null)
25             newNode.random = new RandomListNode(node.random.label);
26         return newNode;
27     }
28 }

2ms

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 3  * class RandomListNode {
 4  *     int label;
 5  *     RandomListNode next, random;
 6  *     RandomListNode(int x) { this.label = x; }
 7  * };
 8  */
 9 public class Solution {
10     public RandomListNode copyRandomList(RandomListNode head) {
11         if(head == null) return head;
12         copyNext(head);
13         copyRandom(head);
14         
15         RandomListNode curr = head;
16         RandomListNode newHead = head.next;
17         RandomListNode start = newHead;
18         while(curr!=null && curr.next!=null){
19             RandomListNode next = curr.next.next;
20             curr.next = next;
21             curr = next;
22             
23             if(start.next!=null) {
24                 start.next = start.next.next;
25                 start = start.next;
26             }
27         }
28         
29         return newHead;
30     }
31     
32     private void copyNext(RandomListNode head){
33         if(head == null) return;
34         
35         RandomListNode curr = head;
36         while(curr!=null){
37             RandomListNode next = curr.next;
38             curr.next = new RandomListNode(curr.label);
39             curr.next.random = curr.random;
40             curr.next.next = next;
41             curr = next;
42         }
43     }
44     
45     private void copyRandom(RandomListNode head) {
46         if(head == null) return;
47         RandomListNode curr = head;
48         while(curr!=null && curr.next!=null){
49             RandomListNode next = curr.next.next;
50             if(curr.next!=null && curr.random!=null){
51                 curr.next.random = curr.random.next;
52             }
53             curr = next;
54         }
55     }
56 }

2ms

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 3  * class RandomListNode {
 4  *     int label;
 5  *     RandomListNode next, random;
 6  *     RandomListNode(int x) { this.label = x; }
 7  * };
 8  */
 9 public class Solution {
10     public RandomListNode copyRandomList(RandomListNode head) 
11     {
12         RandomListNode root = null, prev = null, rootIter = head;
13         
14         while (rootIter != null)
15         {
16             RandomListNode newCopy = new RandomListNode(rootIter.label);
17             newCopy.next = null;
18             newCopy.random = null;
19             
20             prev = rootIter;
21             rootIter = rootIter.next;
22             
23             prev.next = newCopy;
24             newCopy.next = rootIter;
25             /* 'prev' points to previous rootIter whose 'next' will point
26             to the new copy of previous rootIter created in 'newCopy' */
27         }
28         if (head == null)
29             root = null;
30         
31         else
32             root = head.next;
33         
34         rootIter = head;
35         while (rootIter != null)
36         {
37             if (rootIter.random == null)
38                 rootIter.next.random = null;
39             
40             else
41                 rootIter.next.random = rootIter.random.next;
42             
43             rootIter = rootIter.next.next;
44         }
45         
46         rootIter = head;
47         while (rootIter != null)
48         {
49             RandomListNode nextNode = rootIter.next.next;
50             if (nextNode != null)
51                 rootIter.next.next = nextNode.next;
52             
53             rootIter.next = nextNode;
54             rootIter = nextNode;  
55         }
56         return root;
57     }
58 }

3ms

 1 /**
 2  * Definition for singly-linked list with a random pointer.
 3  * class RandomListNode {
 4  *     int label;
 5  *     RandomListNode next, random;
 6  *     RandomListNode(int x) { this.label = x; }
 7  * };
 8  */
 9 public class Solution {
10     
11     private Map<RandomListNode,RandomListNode> visited = new HashMap<>(); 
12     
13     public RandomListNode copyRandomList(RandomListNode head) {
14         if(head == null){
15             return null;
16         }
17         
18         if(visited.containsKey(head)){
19             return visited.get(head); 
20         }
21         
22         RandomListNode newNode = new RandomListNode(head.label); 
23         visited.put(head,newNode); //at this point in time, we have newed this node. does not matter if we need to recurse further to have it fully constructed. this is already copied. thus mark it as visited
24         
25         newNode.next = copyRandomList(head.next); 
26         newNode.random = copyRandomList(head.random); 
27         
28         
29         return newNode; 
30         
31     }
32 }