Remove Nth Node From End of List

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

For 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. Try to do this in one pass.

Solution

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {

        if(head == null || n < 1) return null;

        ListNode fast = head;
        for(int i = 0; i < n; i ++){
            if(fast == null) return head;
            fast = fast.next;
        }

        ListNode slow = head;
        if(fast == null){
            return slow.next;
        }

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

        slow.next = slow.next.next;
        return head;



    }

}