private ListNodeLeet reverseList(ListNodeLeet node2)
{
ListNodeLeet p, prev = null, next;
p = node2;
while (p != null)
{
next = p.next;
p.next = prev;
prev = p;
p = next;
}
return(prev);
}
public ListNodeLeet ReorderList(ListNodeLeet head)
{
// Step 1: Tortoise and hare method to get middle point
ListNodeLeet slow = head, fast = head.next;
while (fast != null && fast.next != null)
{
slow = slow.next;
fast = fast.next.next;
}
// Step 2: Split List
// node1, head of first half 1-> 2-> 3
// node2, head of second half 4 -> 5
ListNodeLeet node1 = slow;
ListNodeLeet node2 = slow.next;
// Step 3: Reverse Second half 5->4
node2 = reverseList(node2);
// Step 4: Merge in result
ListNodeLeet temp = new ListNodeLeet(0);
ListNodeLeet current = temp;
while (node1 != null && node2 != null)
{
if (node1 != null)
{
current.next = node1;
node1 = node1.next;
current = current.next;
}
if (node2 != null)
{
current.next = node2;
node2 = node2.next;
current = current.next;
}
}
return(temp.next);
}