public Element GetKthToLast(Element listHead, int k) // assumption k is an int.
{
Contract.Requires(k >= 1);
Contract.Requires(listHead != null);
// will do it later assert list.Length >= k
var front = listHead;
var kthElement = listHead;
// for k = 1 this loop will not execute.
// for k = 2 this loop will execute once, moving the pointers once apart.
// for k = l this loop will execute l-1 times, moving the pointers l-1 apart.
foreach (int i in Enumerable.Range(1, k-1))
{
if (front.Next == null)
// precondition violation, maybe code contracts?
throw new ArgumentOutOfRangeException($"The length of the of list should be >= {k}. Instead, it is {i}");
front = front.Next;
}
// assert front points to k-th element from front, with n-k elements remaining in front of it.
// assert kthElement points to first element.
// for list of size = 1 and k = 1 (the only allowed), the loop will never execute
// for list of size = 2 and k = 1 there will be 2-1 elements if front of “front”, so the loop will execute once, so the kthElement will move once, so it will point to the second element: correct.
// for list of size = 4 and k = 2 there will be 4-2 elements if front of “front”, so the loop will execute twice, so the kthElement will movetwice, so it will point to the third element: correct.
while (front.Next != null)
{
front = front.Next;
kthElement = kthElement.Next;
}
return kthElement;
}
public Element(object data, Element next)
{
Data = data;
Next = next;
}