算法题：链表反转

node节点：

public class Node {
    Node next;
    Integer value;

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

    public Node addNode(Integer value) {
        Node node = new Node(value);
        this.next = node;
        return node;
    }

    public Node(Integer value, Node next) {
        this.next = next;
        this.value = value;
    }

    public Node getNext() {
        return next;
    }

    public void setNext(Node next) {
        this.next = next;
    }

    public Integer getValue() {
        return value;
    }

    public void setValue(Integer value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Node{" +
                "next=" + next +
                ", value=" + value +
                '}';
    }
}

 main函数：

 Node node1 = new Node(1);
        Node node2 = node1.addNode(2);
        Node node3 = node2.addNode(3);
        Node node4 = node3.addNode(4);
        Node node5 = node4.addNode(5);
        Node node6 = node5.addNode(6);
        Node node7 = node6.addNode(7);

 

1、循环算法：

    private Node reverseNode(Node node1) {
        Node pre = null;
        Node curr = node1;
        Node next;
        while (curr != null) {
            next = curr.next;
            curr.next = pre;
            pre = curr;
            curr = next;
        }
        return pre;
    }

 2、递归算法：

  private Node reverseNode1(Node head) {
        if(head==null || head.next==null){
            return head;
        }
        Node result = reverseNode1(head.next);
        head.next.next=head;
        head.next=null;
        return result;
    }