1 class node(object): 2     def __init__(self,elem=-1,lchild=None,rchild=None): 3         self.elem=elem 4         self.lchild = lchild 5         self.rchild =rchild 6  7  8 class Tree(object): 9     def __init__(self,root=None):10         self.root=root11 12     def add(self,elem):13         nodd =node(elem)14         if self.root==None:15             self.root =nodd16         else:17             queue =[]18             queue.append(self.root)19 20         while queue:21             cur = queue.pop(0)22             if cur.lchild==None:23                 cur.lchild = node24                 return25             elif cur.rchild==None:26                 cur.rchild=node27                 return28             else:29                 queue.append(cur.lchild)30                 queue.append(cur.rchild)