python string re Python string reverse

第一种：使用字符串切片

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

第二种：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'
>>>

第三种：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.

>>>

第四种：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
>>>

第五种：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

>>> s = 'python'
>>> rev(s)
'nohtyp'
>>>

第六种：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'
>>>