在单链表和双链表中删除倒数第k个节点

【题目】在单链表和双链表中删除倒数第k个节点

要求：如果链表长度为N,时间复杂度O(N),额外空间复杂的O(1)

public class DeleteLastKthNode {
	public static class Node {
		public int value;
		public Node next;

		public Node(int value) {
			this.value = value;
		}
	}

	public static class DoubleNode {
		public int value;
		public DoubleNode next;
		public DoubleNode last;

		public DoubleNode(int value) {
			this.value = value;
		}
	}

	public static Node removeLastKthNode(Node head, int k) {
		if (head == null || k < 1) {
			return head;
		}
		Node cur = head;
		while (cur != null) {
			cur = cur.next;
			k--;
		}
		if (k == 0) {
			head = head.next;
		}
		if (k < 0) {
			cur = head;
			while (++k != 0) {
				cur = cur.next;
			}
			cur.next = cur.next.next;

		}
		return head;
	}

	public static DoubleNode removeLastKthDNode(DoubleNode head, int k) {
		if (head == null || k < 1) {
			return head;
		}
		DoubleNode cur = head;
		while (cur != null) {
			k--;
			cur = cur.next;
		}
		if (k == 0) {
			head = head.next;
			head.last = null;
		}
		cur = head;
		if (k < 0) {
			while (++k != 0) {
				cur = cur.next;
			}
			DoubleNode newNext = cur.next.next;
			cur.next = newNext;
			if (newNext != null) {
				newNext.last = cur;
			}
		}
		return head;

	}
}