Python 中的简单回文检查？
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Simple Palindrome check in Python?
提问by user2257342
I am doing a palindrome check program for school, but there is a twist.
我正在为学校做一个回文检查程序，但有一个转折。
Now I already know that I could use a reverse function or something like:
现在我已经知道我可以使用反向函数或类似的东西：
[-1::-1]
However, the program specifically calls for no string slicing or use of the .reverse() function. So, my question is how would I go about doing this if I cannot use these two simple methods?
但是，该程序特别要求不进行字符串切片或使用 .reverse() 函数。所以，我的问题是，如果我不能使用这两种简单的方法，我该怎么做？
回答by georg
You actually don't need any reversefunction at all to check if something is a palindrome. Consider:
您实际上根本不需要任何reverse函数来检查某些东西是否是回文。考虑：
- an empty string is a palindrome
- a string of length 1 is a palindrome
- every other string is a palindrome if its first and last characters are equal and the "middle" part (without the first and the last chars) is a palindrome, recursively.
- 空字符串是回文
- 长度为 1 的字符串是回文
- 如果每个其他字符串的第一个和最后一个字符相等并且“中间”部分（没有第一个和最后一个字符）是一个回文，则每个其他字符串都是一个回文，递归。
Try to implement this in python - it's easy! (Hint: the last char is str[-1]and the middle is str[1:-1]).
尝试在 python 中实现它 - 这很容易！（提示：最后一个字符是str[-1]，中间是str[1:-1]）。
回答by Diego Herranz
It's clear that this is for academic purposes only because using reversed function this code would be trivial.
很明显，这仅用于学术目的，因为使用反向函数此代码将是微不足道的。
def is_palindrome(string):
for i,char in enumerate(string):
if char != string[-i-1]:
return False
return True
>>> is_palindrome('hello')
False
>>> is_palindrome('helloolleh')
True
>>> is_palindrome('')
True
>>> is_palindrome(' ')
True
>>> is_palindrome('a')
True
回答by J0HN
Canonical solution would be:
规范的解决方案是：
def is_palindrome(string):
result = True
str_len = len(string)
for i in range(0, int(str_len/2)): # you need to check only half of the string
if string[i] != string[str_len-i-1]:
result = False
break
return result # single return statement is considered a good practice
