[LeetCode] 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.

最简单的方法是参照clone graph，利用一个HashMap来存储已经访问过的Node。

不使用额外空间的话，可以把复制的node放在原来node之后（第一次遍历）。再把random pointer设到对应的copy node （第二次遍历）。最后还原原来的list和复制的list（第三次遍历）。

/**
* 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 cur = head;

//copy the list, the copied node is appended to its orginal node
while(cur != null){
RandomListNode next = cur.next;
RandomListNode copyNode = new RandomListNode(cur.label);
cur.next = copyNode;
copyNode.next = next;
cur = next;
}

//copy random pointer
cur = head;
while(cur != null){
if(cur.random == null)
cur.next.random = null;
else {
cur.next.random = cur.random.next;
}
cur = cur.next.next;
}

//reorder the list
RandomListNode newListHead = head.next;
RandomListNode newListCur = newListHead;
cur = head;
while(cur != null){
RandomListNode next = cur.next.next;
cur.next = next;
cur = next;

if(next != null){
RandomListNode newListNext = newListCur.next.next;
newListCur.next = newListNext;
newListCur = newListNext;
}
}

return newListHead;
}
}