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.

原题链接：https://oj.leetcode.com/problems/copy-list-with-random-pointer/

题目：给定一个链表，当中的每一个节点包括有一个额外的随机指针指向链表中的随意其它节点或空。

返回链表的一份深度复制。

思路：复制源链表中的每个节点到新链表中(仅仅考虑next)。复制随机指针关系到新链表中(仅仅考虑random.next)，此时新链表的长度是源链表的2倍了。此时修正随机指针为正确的指向关系。

	public RandomListNode copyRandomList(RandomListNode head) {
		if(head == null)
			return null;
		RandomListNode p = head;
		while(p != null){
			RandomListNode copy = new RandomListNode(p.label);
			copy.next = p.next;
			p.next = copy;
			p = copy.next;
		}
		p = head;
		while(p != null){
			if(p.random != null)
				p.next.random = p.random.next;
			p = p.next.next;
		}
		p = head;
		RandomListNode newHead = head.next;
		while(p != null){
			RandomListNode tmp = p.next;
			p.next = tmp.next;
			if(tmp.next != null)
				tmp.next = tmp.next.next;
			p = p.next;
		}
		return newHead;
	}

	// Definition for singly-linked list with a random pointer.
	class RandomListNode {
		int label;
		RandomListNode next, random;

		RandomListNode(int x) {
			this.label = x;
		}
	}