Python实现字符串反转的6种方法

1.使用字符串切片

>>> s = "python"
>>> s[::-1]
'nohtyp'
>>>

2.使用列表的reverse方法

>>> s = "python"
>>> lst = list(s)
>>> lst.reverse()
>>> "".join(lst)
'nohtyp'
>>>

手写 reverse

>>> def reverseString(s:str) -> str:
    lst = list(s)
    i, j = 0, len(s)-1
    while i < j:
        lst[i], lst[j] = lst[j], lst[i]
        i , j = i + 1, j - 1
    return "".join(lst)
 
>>> s = 'python'
>>> reverseString(s)
'nohtyp'
>>>

3.使用reduce

>>> from functools import reduce  # Python3 中不可以直接调用reduce
>>> s = "python"
>>> reduce(lambda x, y: y+x, s)
'nohtyp'
>>>

reduce 函数帮助：

>>> help(reduce)
Help on built-in function reduce in module _functools:
 
reduce(...)
    reduce(function, sequence[, initial]) -> value
     
    Apply a function of two arguments cumulatively to the items of a sequence,
    from left to right, so as to reduce the sequence to a single value.
    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
    of the sequence in the calculation, and serves as a default when the
    sequence is empty.
 
>>>

4.使用递归函数

>>> def reverse(s):
    if s == "":
        return s
    else:
        return reverse(s[1:]) + s[0]
 
     
>>> reverse('python')
'nohtyp'
>>>

python中默认的最大递归数：

>>> import sys
>>> sys.getrecursionlimit()
1000
>>>

5.使用栈

>>> def rev(s):
    lst = list(s) # 转换成list
    ret = ""
    while len(lst):
        ret += lst.pop() # 每次弹出最后的元素
    return ret
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>>> s = 'python'
>>> rev(s)
'nohtyp'
>>>

6.for循环

>>> def rever(s):
    ret = ""
    for i in range(len(s)-1, 0, -1):
        ret += s[i]
    return ret
 
>>> s = "python"
>>> rev(s)
'nohtyp'
>>>