剑指offer-36.二叉搜索树与双向链表-中序遍历

package JianZhioffer;
//剑指 Offer 36. 二叉搜索树与双向链表
/**
 * 输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的循环双向链表。要求不能创建任何新的节点，只能调整树中节点指针的指向。
 */
//中序遍历，二叉搜索树，中序遍历从小到大
import java.util.LinkedList;
import java.util.Queue;

public class test36 {
    static class Node {
        public int val;
        public Node left;
        public Node right;
    
        public Node() {}
    
        public Node(int _val) {
            val = _val;
        }
    
        public Node(int _val,Node _left,Node _right) {
            val = _val;
            left = _left;
            right = _right;
        }
    };
    public static void main(String[] args) {
        Node root=new Node(4);
        root.left=new Node(2);
        root.right=new Node(5);
        root.left.left=new Node(1);
        root.left.right=new Node(3);
        Node result=treeToDoublyList(root);
    }
    public static Node treeToDoublyList(Node root) {
        if(root==null){
            return null;
        }
        Queue<Node> q=new LinkedList<>();
        dfs(root, q);
        Node head=q.poll();
        Node pre=head,curr=null;
        while(!q.isEmpty()){
            curr=q.poll();
            curr.left=pre;
            pre.right=curr;
            curr=curr.right;
            pre=pre.right;
        }
        head.left=pre;
        pre.right=head;
        return head;
    }
    public static void dfs(Node root,Queue<Node> que){
        if(root==null){
            return;
        }
        
        dfs(root.left, que);
        que.offer(root);
        dfs(root.right, que);
        
    }

    
}