没有 for 或 while 循环的字典递归答案

【问题标题】：Dict recursion without for or while loop没有 for 或 while 循环的字典递归
【发布时间】：2018-12-26 21:03:08
【问题描述】：

我对 python 还很陌生，而且我已经对你们中的许多人可能会觉得小菜一碟提出了挑战。输出必须是：

The Monkey-child could not fall asleep, so the mother told him a story, he was once a Tiger-child
  The Tiger-child could not fall asleep, so the mother told him a story, he was once a Human-child
    The Human-child could not fall asleep, so the mother told him a story, he was once a Panther-child
      The Panther-child could not fall asleep, so the mother told him a story, he was once a Snake-child
      The Snake-child has tired and fell asleep
     The Panther-child has tired and fell asleep
    The Human-child has tired and fell asleep
   The Tiger-child has tired and fell asleep
  The Monkey-child has tired and fell asleep

修改代码如下（for 和while 不允许循环）：

 import sys

 StorySequence = {
     "Monkey": "Tiger",
     "Tiger": "Human",
     "Panther": "Snake",
     "Snake": "",
     "Human": "Panther"
 }

 def writePaddingForDepth(depth):
     for i in range(0, depth):
         sys.stdout.write('  ')
         sys.stdout.flush()

 def endStory(thread, depth):
     writePaddingForDepth(depth)
     print ("The " + thread + "-child has tired and fell asleep.")
     return True

 def startStory(thread, depth):
    if (len(StorySequence[thread]) == 0):
        return endStory(thread, depth)

 writePaddingForDepth(depth)

 print ("The " + thread + "-child could not fall asleep, "
        "so the mother told him a story, he was once "
        + StorySequence[thread] + "-child")

 ## Code here

 startStory("Monkey", 0)

如果它是 C 中的数组，我试图处理它，但显然不是，据我所知，它是 dict 类型，这对我来说是全新的东西。我想知道在这个例子中如何在没有for 或while 循环的情况下实现递归。

【问题讨论】：

标签： python recursion

【解决方案1】：

而不是做

for i in range(0, depth):
 sys.stdout.write('  ')

要打印两倍于 depth 的空格数，您可以这样做

sys.stdout.write('  ' * depth)

你可以做类似的事情

def fn(who, depth):
  if(who in StorySequence):
    if(StorySequence[who]!=''):
      print ("\t" * depth + "The " + who + "-child could not fall asleep, "
          "so the mother told him a story, he was once "
          + StorySequence[who] + "-child")
      fn(StorySequence[who], depth+1)
    print ("\t" * depth + "The " + who + "-child has tired and fell asleep.")

fn("Monkey", 0)

递归函数必须有退出条件以防止它成为无限递归。

这里，只有在字典中有一个有效的键并且值不是空字符串时才会进行递归。

who in StorySequence 用于检查字典StorySequence 中是否存在具有who 内容的键。

【讨论】：