/// <summary>
/// two steps:
/// First step, make a copy a list, and also build a hashmap between nodes in
/// the original linked list to the copy list
/// Second step, copy random point for the list
/// </summary>
/// <param name="head"></param>
/// <returns></returns>
public static RandomListNode CopyRandomList(RandomListNode head)
{
if (head == null)
{
return(null);
}
var dict = new Dictionary <RandomListNode, RandomListNode>();
var copyHead = copyListWithoutRandom(head, dict);
copyRandomPointer(head, dict);
return(copyHead);
}
/// <summary>
/// use recursive function to shorten the time
/// </summary>
/// <param name="head"></param>
/// <param name="dict"></param>
/// <returns></returns>
private static RandomListNode copyListWithoutRandom(RandomListNode head, Dictionary <RandomListNode, RandomListNode> dict)
{
if (head == null)
{
return(null);
}
var value = head.label;
var copyHead = new RandomListNode(value);
dict.Add(head, copyHead);
copyHead.next = copyListWithoutRandom(head.next, dict);
return(copyHead);
}
private static void copyRandomPointer(RandomListNode head, Dictionary <RandomListNode, RandomListNode> dict)
{
while (head != null)
{
var random = head.random;
if (random != null)
{
dict[head].random = dict[random];
}
else
{
dict[head].random = null;
}
head = head.next;
}
}
