Leetcode Copy List with Random Pointer 拷贝链表

题目：

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.

分析：

1. 遍历链表，拷贝链表的每一个节点，并用HashMap记录原来的节点和拷贝的节点的对应关系。

2. 再次遍历链表，把拷贝的节点连接起来，并加上random节点的关系。

Java代码实现：

/**
* 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;

HashMap<RandomListNode, RandomListNode> nodes = new HashMap<RandomListNode, RandomListNode>();
RandomListNode node = head;
RandomListNode newHead = new RandomListNode(head.label);
nodes.put(node, newHead);
node = node.next;
while(node!=null)
{
nodes.put(node, new RandomListNode(node.label));
node = node.next;
}
node = head;
RandomListNode temp = newHead;
temp.random = nodes.get(node.random);
while(node!=null)
{
temp.next = nodes.get(node.next);
node = node.next;
temp = temp.next;
if(temp!=null)
temp.random = nodes.get(node.random);
}
return newHead;
}
}