/*
1. 题目要求可以转换成将一个树的inorder 按从左到右的顺序输出
2. 开始读错题了，应该是next函数要O（1）的时间，O（h）空间， 所以可以预处理一下
3. 按照 迭代法 求中序遍历去做即可

*/


/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class BSTIterator {


    Stack<TreeNode> stack;

    public BSTIterator(TreeNode root) {
        stack = new Stack<TreeNode>();
        scanLeft(root);
    }

    private void scanLeft(TreeNode root){
        while (root != null){
            stack.push(root);
            root = root.left;
        }
    }

    /** @return the next smallest number */
    public int next() {
        var node = stack.pop();
        scanLeft(node.right);
        return node.val;
    }

    /** @return whether we have a next smallest number */
    public boolean hasNext() {
        return !stack.isEmpty();
    }
}

/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator obj = new BSTIterator(root);
 * int param_1 = obj.next();
 * boolean param_2 = obj.hasNext();
 */