# -*- coding=utf-8 -*-


class Node(object):
 """节点类"""

 def __init__(self, element=-1, l_child=None, r_child=None):
  self.element = element
  self.l_child = l_child
  self.r_child = r_child


class Tree(object):
 """树类"""

 def __init__(self):
  self.root = Node()
  self.queue = []

 def add_node(self, element):
  """为树添加节点"""

  node = Node(element)
  # 如果树是空的，则对根节点赋值
  if self.root.element == -1:
   self.root = node
   self.queue.append(self.root)
  else:
   tree_node = self.queue[0]
   # 此结点没有左子树，则创建左子树节点
   if tree_node.l_child is None:
    tree_node.l_child = node
    self.queue.append(tree_node.l_child)
   else:
    tree_node.r_child = node
    self.queue.append(tree_node.r_child)
    # 如果该结点存在右子树，将此节点丢弃
    self.queue.pop(0)

 def front_recursion(self, root):
  """利用递归实现树的前序遍历"""

  if root is None:
   return

  print root.element,
  self.front_recursion(root.l_child)
  self.front_recursion(root.r_child)

 def middle_recursion(self, root):
  """利用递归实现树的中序遍历"""

  if root is None:
   return

  self.middle_recursion(root.l_child)
  print root.element,
  self.middle_recursion(root.r_child)

 def back_recursion(self, root):
  """利用递归实现树的后序遍历"""

  if root is None:
   return

  self.back_recursion(root.l_child)
  self.back_recursion(root.r_child)
  print root.element,

 @staticmethod
 def front_stack(root):
  """利用堆栈实现树的前序遍历"""

  if root is None:
   return

  stack = []
  node = root
  while node or stack:
   # 从根节点开始，一直找它的左子树
   while node:
    print node.element,
    stack.append(node)
    node = node.l_child
   # 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 = stack.pop()
   # 开始查看它的右子树
   node = node.r_child

 @staticmethod
 def middle_stack(root):
  """利用堆栈实现树的中序遍历"""

  if root is None:
   return

  stack = []
  node = root
  while node or stack:
   # 从根节点开始，一直找它的左子树
   while node:
    stack.append(node)
    node = node.l_child
   # 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 = stack.pop()
   print node.element,
   # 开始查看它的右子树
   node = node.r_child

 @staticmethod
 def back_stack(root):
  """利用堆栈实现树的后序遍历"""

  if root is None:
   return

  stack1 = []
  stack2 = []
  node = root
  stack1.append(node)
  # 这个while循环的功能是找出后序遍历的逆序，存在stack2里面
  while stack1:
   node = stack1.pop()
   if node.l_child:
    stack1.append(node.l_child)
   if node.r_child:
    stack1.append(node.r_child)
   stack2.append(node)
  # 将stack2中的元素出栈，即为后序遍历次序
  while stack2:
   print stack2.pop().element,

 @staticmethod
 def level_queue(root):
  """利用队列实现树的层次遍历"""

  if root is None:
   return

  queue = []
  node = root
  queue.append(node)
  while queue:
   node = queue.pop(0)
   print node.element,
   if node.l_child is not None:
    queue.append(node.l_child)
   if node.r_child is not None:
    queue.append(node.r_child)


if __name__ == '__main__':
 """主函数"""

 # 生成十个数据作为树节点
 elements = range(10)
 tree = Tree()
 for elem in elements:
  tree.add_node(elem)

 print '队列实现层次遍历:'
 tree.level_queue(tree.root)

 print '\n\n递归实现前序遍历:'
 tree.front_recursion(tree.root)
 print '\n递归实现中序遍历:'
 tree.middle_recursion(tree.root)
 print '\n递归实现后序遍历:'
 tree.back_recursion(tree.root)

 print '\n\n堆栈实现前序遍历:'
 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.back_stack(tree.root)