// O(n) mem and O(1) space
public RandomNode DeepCopy2(RandomNode head)
{
if (head == null)
{
return(null);
}
var cur = head;
// copy and insert new node right after the old node
// 1 -> 2 -> 3 becomes 1 -> 1 -> 2 -> 2 -> 3 -> 3
while (cur.next != null)
{
var newnode = new RandomNode(cur.value);
newnode.next = cur.next;
cur.next = newnode;
cur = newnode.next;
}
// Copy random link
cur = head;
while (cur.next != null)
{
cur.next.random = cur.random.next;
cur = cur.next.next;
}
// Detach new list;
// 1 -> 1 -> 2 -> 2 -> 3 -> 3 becomes two copies of 1 -> 2 -> 3
cur = head;
var newhead = cur.next;
var newcur = newhead;
while (cur.next != null)
{
cur.next = cur.next.next;
newcur.next = newcur.next.next;
}
return(newhead);
}
// O(n) mem and space
public RandomNode DeepCopy(RandomNode head)
{
if (head == null)
{
return(null);
}
RandomNode newhead = new RandomNode(head.value);
var dictionary = new Dictionary <RandomNode, RandomNode>();
dictionary.Add(head, newhead);
var cur = head;
var newcur = newhead;
// copy
while (cur.next != null)
{
newcur.next = new RandomNode(cur.next.value);
newcur = newcur.next;
cur = cur.next;
dictionary.Add(cur, newcur);
}
// Restore
cur = head;
newcur = newhead;
while (cur != null)
{
if (cur.random != null)
{
newcur.random = dictionary[cur.random];
}
newcur = newcur.next;
cur = cur.next;
}
return(newhead);
}