Given the head of a linked list, remove the nth node from the end of the list and return its head.

**Follow up:** Could you do this in one pass?

**Example 1:**

**Input:** head = [1,2,3,4,5], n = 2
**Output:** [1,2,3,5]

**Example 2:**

**Input:** head = [1], n = 1
**Output:** []

**Example 3:**

**Input:** head = [1,2], n = 1
**Output:** [1]

**Constraints:**

The number of nodes in the list is sz.

1 <= sz <= 30

0 <= Node.val <= 100

1 <= n <= sz

Solution:

**Approach 1:**

```
class Solution {
public ListNode removeNthFromEnd(ListNode head, int n)
{
int length=0;
ListNode dummy=head;
while(dummy!=null)
{
length++;
dummy=dummy.next;
}
if(n>length) return dummy;
if(n==length) return head.next;
length-=n;
dummy=head;
while(length>1 && dummy.next!=null)
{
dummy=dummy.next;
length--;
}
dummy.next=dummy.next.next;
return head;
}
}
```

**Approach 2:**

```
class Solution {
public ListNode removeNthFromEnd(ListNode head, int n) {
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode fast = dummy;
ListNode slow = dummy;
for (int i = 1; i <= n + 1; i++) {
fast = fast.next;
}
while (fast != null) {
fast = fast.next;
slow = slow.next;
}
slow.next = slow.next.next;
return dummy.next;
}
}
```

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