leetcode173

class BSTIterator:
    def __init__(self, root: TreeNode):
        self.lists = []
        self.idx = 0
        self.size = 0
        self.inOrder(root)
        
    def inOrder(self,root):
        if root != None:
            if root.left != None:
                self.inOrder(root.left)
            self.lists.append(root.val)
            self.size += 1
            if root.right != None:
                self.inOrder(root.right)

    def next(self) -> int:
        """
        @return the next smallest number
        """
        if self.hasNext():
            v = self.lists[self.idx]
            self.idx += 1
            return v
        else:
            return -1
        
    def hasNext(self) -> bool:
        """
        @return whether we have a next smallest number
        """
        return self.idx < self.size