7.1：链表反转

7.1：链表反转

 

链表反转注意：返回头部节点。 

 

单链表的反转

//  head
    //   a    ->   b    ->  c  ->  null
    //   c    ->   b    ->  a  ->  null
    public static Node reverseLinkedList(Node head) {
        Node pre = null;
        Node next = null;
        while (head != null) {
            next = head.next;
            head.next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }

 

 

双向链表的反转

public static DoubleNode reverseDoubleList(DoubleNode head) {
        DoubleNode pre = null;
        DoubleNode next = null;
        while (head != null) {
            next = head.next;
            head.next = pre;
            head.last = next;
            pre = head;
            head = next;
        }
        return pre;
    }