反转单向链表和双向链表

单项链表
找到当前头结点前一个节点
把下一个节点设置成头结点
把原来头结点设置成当前头结点的下一个节点

class Node1{
	int value;
	Node1 next;
	public Node1(int data) {
		this.value = data;
	}
}
	public Node1 reverse(Node1 head) {
		Node1 pre = null;
		Node1 next = null;
		while (head != null) {
			next = head.next;
			head.next = pre;
			pre = head;
			head = next;
		}
		return pre;
	}

双向链表
找到当前头结点的前一个节点和下一个节点
下一个节点变成头结点
把原来头结点变成当前头结点的下一个节点

class DoubleNode{
	public int value;
	public DoubleNode last;
	public DoubleNode next;
	public DoubleNode (int data) {
		this.value = data;
	}
}
	public Node reverseDoubleLinkedList(Node head) {
		DoubleNode pre = null;
		DoubleNode next = null;
		while (head != null) {
			next = head.next;
			head.next = pre;
			head.last = next;
			pre = head;
			head = next;
		}
	}