19. 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.

 

public ListNode removeNthFromEnd(ListNode head, int n) {
  ListNode dummy = new ListNode(-1);
  ListNode slow = dummy;
  ListNode fast = dummy;
  dummy.next = head; //0的下一个结点是head
  for (int i = 1; i <= n + 1; i++)
    if (fast.next != null) {
      fast = fast.next; //fast先往前移动n+1
    } else {
      return null;
    }
  while (fast != null) {
    slow = slow.next;
    fast = fast.next;
  }
  slow.next = slow.next.next;
  return dummy.next;
}