Leetcode：Copy List with Random Pointer

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.

解析：深拷贝一个链表，链表里的节点有两个指针，一个指向next一个是指向random元素。大致解法有两种：

1. 使用HashMap，记录源节点与新节点的对应关系，或者源节点与next的关系，或者源节点与random的关系。

2.直接在源节点后面复制源节点，random也是指向源节点random的next，然后分割链表即可。

代码：

/**
* 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 null;

RandomListNode dummy = new RandomListNode(0);
RandomListNode node1 = head;
RandomListNode node2 = dummy;
HashMap<RandomListNode,RandomListNode> map = new HashMap<RandomListNode,RandomListNode>();

while(node1!=null)
{
RandomListNode copynode = new RandomListNode(node1.label);
copynode.random = node1;
node2.next = copynode;
map.put(node1,node1.next);
RandomListNode tmp = node1;
node1 = node1.next;
tmp.next = copynode;
node2 = node2.next;
}

node2 = dummy.next;
while(node2!=null)
{
if(node2.random.random!=null)node2.random = node2.random.random.next;
else node2.random = null;
node2 = node2.next;
}

node1 = head;
while(node1!=null)
{
node1.next = map.get(node1);
node1 = node1.next;
}

return dummy.next;
}
}

    

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