LeetCode: Remove Nth Node From End Of List Solution

Approach

Two pointers here is to maintain the position

Target el is n dist from tail

fast and slow start from head

First, fast will iterate n time

so fast is n dist from head (which is also slow)
aka, slow is n dist from fast

Then, fast and slow will both iterate until fast reach tail

because target el is n dist from tail
and slow is n dist from fast, so the same

Now slow is pointed to target, remove that

Implementation

1// no fair-play
2var removeNthFromEnd = function (head, n) {
3  let iter = head
4  let arr = []
5  while (iter) {
6    arr.push(iter.val)
7    iter = iter.next
8  }
9  n = arr.length - n
10  arr.splice(n, 1)
11  arr = arr.map(el => new ListNode(el))
12  for (let i = 0; i < arr.length - 1; i++) {
13    arr[i].next = arr[i + 1]
14  }
15  return arr[0] || null
16}
17
18var removeNthFromEnd = function (head, n) {
19  let fast = (slow = head)
20  while (n--) {
21    fast = fast.next
22  }
23  if (!fast) {
24    return head.next
25  }
26  while (fast.next) {
27    fast = fast.next
28    slow = slow.next
29  }
30  slow.next = slow.next.next
31  return head
32}