我创建了一个类Tree和一个Node类.现在我需要实现preOrder,postorder和inorder遍历.我是用私人功能做的.但有没有办法只使用一个函数来做同样的事情?
class Node: def __init__(self,data): self.left = None self.right = None self.data = data class Tree: def __init__(self): self.root = None # Private helper functions def __insert(self,data,root): if data < root.data: if root.left is None: root.left = Node(data) else: self.__insert(data,root.left) elif data >= root.data: if root.right is None: root.right = Node(data) else: self.__insert(data,root.right) # Traversals def __preOrder(self,root): print root.data if root.left: self.__preOrder(root.left) if root.right: self.__preOrder(root.right) # Wrapper Functions def insert(self,data): if self.root == None: self.root = Node(data) else: self.__insert(data,self.root) def preOrder(self): self.__preOrder(self.root) tree = Tree() print "Enter elements to be inserted in the tree(End with a -1): " while True: elem = int(raw_input()) if elem == -1: break tree.insert(elem) print "Preorder traversal: " tree.preOrder()
解决方法
是的,您可以在单个函数中实现所有3种类型的遍历.我已经将遍历函数转换为生成器,以使它们更加通用.因此,它们不是打印数据,而是生成数据的迭代器.这使您可以在数据生成时处理数据,也可以将数据捕获到列表(或其他集合)中.
在Python 2中,您的类应该继承自object,否则您将获得旧式类,与新式类相比,它们相当有限(Python 3只有新式类).
顺便说一句,没有必要为私有函数(调用Python的name-mangling机制)使用双下划线,单个前导下划线就足够了.
我还在类中添加了简单的__repr__方法,这在开发过程中非常方便.调试.
class Node(object): def __init__(self,data): self.left = None self.right = None self.data = data def __repr__(self): return repr((self.data,self.left,self.right)) class Tree(object): def __init__(self): self.root = None def __repr__(self): return repr(self.root) # Private helper functions def _insert(self,root): if data < root.data: if root.left is None: root.left = Node(data) else: self._insert(data,root.left) else: # data >= root.data: if root.right is None: root.right = Node(data) else: self._insert(data,root.right) def _traverse(self,root,mode): if mode == 'pre': yield root.data if root.left: for u in self._traverse(root.left,mode): yield u if mode == 'in': yield root.data if root.right: for u in self._traverse(root.right,mode): yield u if mode == 'post': yield root.data # Wrapper Functions def insert(self,data): if self.root == None: self.root = Node(data) else: self._insert(data,self.root) def preOrder(self): for u in self._traverse(self.root,'pre'): yield u def inorder(self): for u in self._traverse(self.root,'in'): yield u def postorder(self): for u in self._traverse(self.root,'post'): yield u # Test tree = Tree() for elem in '31415926': tree.insert(elem) print tree print "Preorder traversal: " print list(tree.preOrder()) print "Inorder Traversal: " print list(tree.inorder()) print "postorder Traversal: " print list(tree.postorder())
产量
('3',('1',None,('2',None))),('4',('5',('9',('6',None),None)))) Preorder traversal: ['3','1','2','4','5','9','6'] Inorder Traversal: ['1','3','6','9'] postorder Traversal: ['2','3']
以下是处理数据时的示例:
for data in tree.inorder(): print data
FWIW,这段代码在Python 3中会更加清晰,因为我们可以使用语法的yield而不是for循环.而不是
for u in self._traverse(root.left,mode): yield u
我们能做到
yield from self._traverse(root.left,mode)