python 按图形打印二叉树

需求：

python代码实现
1. 按层打印二叉树
2. 需要打印二叉树层与层之间的斜线
3. 结点的下一层如果没有子节点，以‘N’代替

方法：

1. 使用namedtuple表示二叉树
2. 使用StringIO方法，遍历时写入结果，最后打印出结果
3. 打印结点值时，如果为空，StringIO（）写入‘N ’
4. 递归获取树的深度
5. 将遍历树时候每层的node当做list元素存入list中
6. 根据树的深度设置每层node应该pad的空格数量：
   2 **（深度-1）-1
7. 打印每层之间的斜线，需处理：
   
   • 每两层之间的斜线应有 “2 **（深度-1）”层
   • 每层的左斜线与右斜线之间的空格数量有变化，每深一层加2

python代码：

#!/usr/bin/env python3# -*- coding: utf-8 -*-from collections import namedtuplefrom io import StringIOimport math# define the node structureNode = namedtuple('Node', ['data', 'left', 'right'])# initialize the treetree = Node(1,            Node(2,                 Node(4,                      Node(7, None, None),                      None),                 Node(5, None, None)),            Node(3,                 Node(6,                      Node(8, None, None),                      Node(9, None, None)),                 None))class Queue(object):    def __init__(self):        self.queue = []    def enqueue(self, b):        self.queue.insert(0, b)    def dequeue(self):        return self.queue.pop()    def isEmpty(self):        return self.queue == []def getheight(node):    if not node:        return 0    else:        return max(getheight(node.left), getheight(node.right)) + 1def add_padding(str, pad_length_value):    str = str.strip()    return str.center(pad_length_value, ' ')# sotre node , space and slashes in list first, then print outdef pretty_print(tree):    output = StringIO()    pretty_output = StringIO()    current_level = Queue()    next_level = Queue()    current_level.enqueue(tree)    depth = 0    # get the depth of current tree    # get the tree node data and store in list    if tree:        while not current_level.isEmpty():            current_node = current_level.dequeue()            output.write('%s ' % current_node.data if current_node else 'N ')            next_level.enqueue(                current_node.left if current_node else current_node)            next_level.enqueue(                current_node.right if current_node else current_node)            if current_level.isEmpty():                if sum([i is not None for i in next_level.queue]                       ):  # if next level has node                    current_level, next_level = next_level, current_level                    depth = depth + 1                output.write('\n')    print('the tree print level by level is :')    print(output.getvalue())    print("current tree's depth is %i" % (depth+1))    # add space to each node    output.seek(0)    pad_length = 3    keys = []    spaces = int(math.pow(2, depth))    while spaces > 0:        skip_start = spaces * pad_length        skip_mid = (2 * spaces - 1) * pad_length        key_start_spacing = ' ' * skip_start        key_mid_spacing = ' ' * skip_mid        keys = output.readline().split(' ')  # read one level to parse        padded_keys = (add_padding(key, pad_length) for key in keys)        padded_str = key_mid_spacing.join(padded_keys)        complete_str = ''.join([key_start_spacing, padded_str])        pretty_output.write(complete_str)        # add space and slashes to middle layer        slashes_depth = spaces        print('current slashes depth im_resize:')        print(spaces)        print("current levle's list is:")        print(keys)        spaces = spaces // 2        if spaces > 0:            pretty_output.write('\n')  # print '\n' each level            cnt = 0            while cnt < slashes_depth:                inter_symbol_spacing = ' ' * (pad_length + 2 * cnt)                symbol = ''.join(['/', inter_symbol_spacing, '\\'])                symbol_start_spacing = ' ' * (skip_start-cnt-1)                symbol_mid_spacing = ' ' * (skip_mid-2*(cnt+1))                pretty_output.write(''.join([symbol_start_spacing, symbol]))                for i in keys[1:-1]:                    pretty_output.write(''.join([symbol_mid_spacing, symbol]))                pretty_output.write('\n')                cnt = cnt + 1    print(pretty_output.getvalue())if __name__ == '__main__':    pretty_print(tree)

测试用的tree如下：

运行结果如下：

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参考：
StringIO 模块用于在内存缓冲区中读写数据

http://stackoverflow.com/questions/13484943/print-a-binary-tree-in-a-pretty-way

http://articles.leetcode.com/how-to-pretty-print-binary-tree/#comment-114851