138. Copy List with Random Pointer

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.

与图拷贝的方法类似，使用map的方式进行处理，但是也有不同，图拷贝是线拷贝点，然后是边；链表可以直接在一个循环中统一处理。

java

/** * Definition for singly-linked list with a random pointer. * class RandomListNode { *     int label; *     RandomListNode next, random; *     RandomListNode(int x) { this.label = x; } * }; */public class Solution {    public RandomListNode copyRandomList(RandomListNode head) {        if (head == null) {            return head;        }        Map<RandomListNode, RandomListNode> map = new HashMap<>();        RandomListNode dummy = new RandomListNode(0);        RandomListNode pre = dummy;        RandomListNode node;        while (head != null) {            if (map.containsKey(head)) {                node = map.get(head);            } else {                node = new RandomListNode(head.label);                map.put(head, node);            }            pre.next = node;            if (head.random != null) {                if (map.containsKey(head.random)) {                    node.random = map.get(head.random);                } else {                    node.random = new RandomListNode(head.random.label);                    map.put(head.random, node.random);                }             }            pre = pre.next;            head = head.next;        }        return dummy.next;    }}

python

# Definition for singly-linked list with a random pointer.# class RandomListNode(object):#     def __init__(self, x):#         self.label = x#         self.next = None#         self.random = Noneclass Solution(object):    def copyRandomList(self, head):        """        :type head: RandomListNode        :rtype: RandomListNode        """        if head is None:            return head        mapping = {}        dummy = RandomListNode(0)        pre, node = dummy, head        while head is not None:            if head in mapping:                node = mapping[head]            else:                node = RandomListNode(head.label)                mapping[head] = node            pre.next = node            if head.random is not None:                if head.random in mapping:                    node.random = mapping[head.random]                else:                    node.random = RandomListNode(head.random.label)                    mapping[head.random] = node.random            pre = pre.next            head = head.next        return dummy.next