public RandomListNode CopyRandomListOptimized(RandomListNode head)
{
var runner = head;
while (runner != null)
{
var copy = new RandomListNode(runner.label);
copy.next = runner.next;
runner.next = copy;
runner = copy.next;
}
var ptr = head;
while (ptr != null)
{
ptr.next.random = ptr.random?.next;
ptr = ptr.next.next;
}
var ptr_old_list = head; // A->B->C
var ptr_new_list = head.next; // A'->B'->C'
var head_old = head.next;
while (ptr_old_list != null)
{
ptr_old_list.next = ptr_old_list.next.next;
ptr_new_list.next = (ptr_new_list.next != null) ? ptr_new_list.next.next : null;
ptr_old_list = ptr_old_list.next;
ptr_new_list = ptr_new_list.next;
}
return(head_old);
}
public RandomListNode CopyRandomList(RandomListNode head)
{
var randomMap = new Dictionary <RandomListNode, RandomListNode>();
var copyMap = new Dictionary <RandomListNode, RandomListNode>();
var copyRunner = new RandomListNode(-1);
var copyHead = copyRunner;
var runner = head;
while (runner != null)
{
var copy = new RandomListNode(runner.label);
copyMap[copy] = runner;
randomMap[runner] = runner.random;
copyRunner.next = copy;
copyRunner = copyRunner.next;
runner = runner.next;
}
var copyListHead = copyHead.next;
runner = copyListHead;
while (runner != null)
{
var current = runner;
var original = copyMap[current];
var originalRandom = randomMap[original];
var copyRandom = copyMap.FirstOrDefault(kv => kv.Value == originalRandom).Key;
runner.random = copyRandom;
runner = runner.next;
}
return(copyListHead);
}