Python编程实现二叉树及七种遍历方法详解

#coding=utf-8class Node(object):  """节点类"""  def __init__(self, elem=-1, lchild=None, rchild=None):    self.elem = elem    self.lchild = lchild    self.rchild = rchildclass Tree(object):  """树类"""  def __init__(self):    self.root = Node()    self.myQueue = []  def add(self, elem):    """为树添加节点"""    node = Node(elem)    if self.root.elem == -1: # 如果树是空的，则对根节点赋值      self.root = node      self.myQueue.append(self.root)    else:      treeNode = self.myQueue[0] # 此结点的子树还没有齐。      if treeNode.lchild == None:        treeNode.lchild = node        self.myQueue.append(treeNode.lchild)      else:        treeNode.rchild = node        self.myQueue.append(treeNode.rchild)        self.myQueue.pop(0) # 如果该结点存在右子树，将此结点丢弃。  def front_digui(self, root):    """利用递归实现树的先序遍历"""    if root == None:      return    print root.elem,    self.front_digui(root.lchild)    self.front_digui(root.rchild)  def middle_digui(self, root):    """利用递归实现树的中序遍历"""    if root == None:      return    self.middle_digui(root.lchild)    print root.elem,    self.middle_digui(root.rchild)  def later_digui(self, root):    """利用递归实现树的后序遍历"""    if root == None:      return    self.later_digui(root.lchild)    self.later_digui(root.rchild)    print root.elem,  def front_stack(self, root):    """利用堆栈实现树的先序遍历"""    if root == None:      return    myStack = []    node = root    while node or myStack:      while node:           #从根节点开始，一直找它的左子树        print node.elem,        myStack.append(node)        node = node.lchild      node = myStack.pop()      #while结束表示当前节点node为空，即前一个节点没有左子树了      node = node.rchild         #开始查看它的右子树  def middle_stack(self, root):    """利用堆栈实现树的中序遍历"""    if root == None:      return    myStack = []    node = root    while node or myStack:      while node:           #从根节点开始，一直找它的左子树        myStack.append(node)        node = node.lchild      node = myStack.pop()      #while结束表示当前节点node为空，即前一个节点没有左子树了      print node.elem,      node = node.rchild         #开始查看它的右子树  def later_stack(self, root):    """利用堆栈实现树的后序遍历"""    if root == None:      return    myStack1 = []    myStack2 = []    node = root    myStack1.append(node)    while myStack1:          #这个while循环的功能是找出后序遍历的逆序，存在myStack2里面      node = myStack1.pop()      if node.lchild:        myStack1.append(node.lchild)      if node.rchild:        myStack1.append(node.rchild)      myStack2.append(node)    while myStack2:             #将myStack2中的元素出栈，即为后序遍历次序      print myStack2.pop().elem,  def level_queue(self, root):    """利用队列实现树的层次遍历"""    if root == None:      return    myQueue = []    node = root    myQueue.append(node)    while myQueue:      node = myQueue.pop(0)      print node.elem,      if node.lchild != None:        myQueue.append(node.lchild)      if node.rchild != None:        myQueue.append(node.rchild)if __name__ == '__main__':  """主函数"""  elems = range(10)      #生成十个数据作为树节点  tree = Tree()     #新建一个树对象  for elem in elems:    tree.add(elem)      #逐个添加树的节点  print '队列实现层次遍历:'  tree.level_queue(tree.root)  print '/n/n递归实现先序遍历:'  tree.front_digui(tree.root)  print '/n递归实现中序遍历:'  tree.middle_digui(tree.root)  print '/n递归实现后序遍历:'  tree.later_digui(tree.root)  print '/n/n堆栈实现先序遍历:'  tree.front_stack(tree.root)  print '/n堆栈实现中序遍历:'  tree.middle_stack(tree.root)  print '/n堆栈实现后序遍历:'  tree.later_stack(tree.root)