[英]Explanation of Recursive Function in Python
I am new to Python and trying to wrap my head around recursive functions. 我是Python的新手,正在尝试将我的头放在递归函数上。 I am understanding the overall concept but I came across an example that I can't seem to understand fully what it is doing.
我正在理解总体概念,但是遇到了一个例子,我似乎无法完全理解它在做什么。 A step by step breakdown of what is happening would be ideal, appreciate the help in advance.
逐步分解正在发生的事情将是理想的,请提前了解帮助。
def anagrams(s):
if s == '':
return [s]
else:
ans = []
for w in anagrams(s[1:]):
for pos in range(len(w)+1):
ans.append(w[:pos] + s[0] + w[pos:])
return ans
def anagrams(s):
# if argument <s> is a blank String
if s == '':
# return a list is just <s> in it
return [s]
else:
# create a List
ans = []
# for each String character in calling this function recursively,
# but removing character 0!
for w in anagrams(s[1:]):
# for character position number starting at 0 and ending at
# the length of the returned value of the recursed function
# plus 1
for pos in range(len(w)+1):
# append a string with the following concatenation:
# - the returned value's string from position 0 to position <pos>
# - the character at position 0 of <s>
# - the returned value's string from position <pos> to the end
ans.append(w[:pos] + s[0] + w[pos:])
# return the list
return ans
if s == '':
return [s]
If it is a blank string, there are no other anagrams, return a list with only that blank string.. 如果它是空字符串,则没有其他字谜,请返回仅包含该空字符串的列表。
Otherwise, 除此以外,
for w in anagrams(s[1:]):
separate s
to the first character ( s[0]
) and the substring of all other characters ( s[1:]
). 将
s
分隔为第一个字符( s[0]
)和所有其他字符的子字符串( s[1:]
)。 Call the function again to find all anagrams of the substring (those are the w
s), 再次调用该函数以查找子字符串的所有字词(都是
w
),
for pos in range(len(w)+1):
ans.append(w[:pos] + s[0] + w[pos:])
then for each of those, insert the first character of s
in any possible position ( pos
) within w
. 然后针对其中每一个,将
s
的第一个字符插入w
内的任何可能位置( pos
)。
Here is your function with a little print statement that helps to see whats going on. 这是您的函数,带有一些打印语句,可帮助您了解发生了什么。
def anagrams(s):
if s == '':
return [s]
else:
ans = []
level = len(s)
for w in anagrams(s[1:]):
print('level %d, s[0]: %s, w: %s' % (level, s[0], w))
for pos in range(len(w)+1):
ans.append(w[:pos] + s[0] + w[pos:])
return ans
try: 尝试:
1. 1。
anagrams('a')
output: 输出:
level 1, s[0]: a, w:
2. 2。
anagrams('ba')
output: 输出:
level 1, s[0]: a, w:
level 2, s[0]: b, w: a
3. 3。
anagrams('cba')
level 1, s[0]: a, w:
level 2, s[0]: b, w: a
level 3, s[0]: c, w: ba
level 3, s[0]: c, w: ab
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