19. Remove Nth Node From End of List

Problem:

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

Example:

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:

Given n will always be valid.

Analysis:

2 pointers. fast is n nodes away from slow. 

Solution:

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

        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }
        
        slow.next = slow.next.next;
        return dummy.next;
    } 
}