class Solution(object):
def reverseString(self, s):
"""
:type s: List[str]
:rtype: None Do not return anything, modify s in-place instead.
"""
left = 0
right = len(s)-1
while left <= right:
s[left], s[right] = s[right], s[left]
left += 1
right -= 1
class Solution(object):
def reverseStr(self, s, k):
"""
:type s: str
:type k: int
:rtype: str
"""
s = list(s)
for i in range(0, len(s), 2*k):
s[i:(k+i)]=self.reverse(s[i:(k+i)])
#print(s)
return ''.join(s)
def reverse(self, s):
left = 0
right = len(s)-1
while left <= right:
s[left], s[right] = s[right], s[left]
left += 1
right -= 1
return s
class Solution:
def replaceSpace(self, s: str) -> str:
s = list(s)
for i in range(len(s)):
if s[i] == ' ':
s[i] = "%20"
return ''.join(s)
class Solution(object):
def replaceSpace(self, s):
"""
:type s: str
:rtype: str
"""
return "%20".join(s.split(" "))
class Solution:
def replaceSpace(self, s: str) -> str:
return s.replace(' ', '%20')
class Solution:
def reverseWords(self, s: str) -> str:
return ' '.join(s.split()[::-1])
class Solution(object):
def reverseLeftWords(self, s, n):
"""
:type s: str
:type n: int
:rtype: str
"""
s = list(s)
while n > 0:
s.append(s.pop(0))
n -= 1
return ''.join(s)
class Solution:
def reverseLeftWords(self, s: str, n: int) -> str:
return s[n:] + s[:n]
class Solution:
def reverseLeftWords(self, s: str, n: int) -> str:
s = list(s)
s[:n] = reversed(s[:n])
#print(reversed(s[:n]))
s[n:] = reversed(s[n:])
s.reverse()
return ''.join(s)
注意:
- 图三,最后不可用reversed(s),因为reversed()返回的是一个反转迭代器,可以尝试uncomment print语句看一下输出;
- 也就是说,在经过reversed()的作用之后,返回的是一个把序列值经过反转之后的迭代器,所以,需要通过遍历,或者List, 或者next()等方法,获取作用后的值。
- reversed()可以用在list, tuple, string
- .reverse()则是反转原列表,只可用于list
插入知识点:
切片是值传递,数组是引用传递,也就是切片是造了一个新的局部变量,只在调用这个函数的栈里有效。(From c++鲁智深)
class Solution(object):
def reverseLeftWords(self, s, n):
"""
:type s: str
:type n: int
:rtype: str
"""
s = list(s)
end = len(s) - 1
self.reverseHelper(s, 0, n - 1)
self.reverseHelper(s, n, end)
self.reverseHelper(s, 0, end)
return ''.join(s)
#手动实现内置reversed函数,这样就跟图三一个解法
def reverseHelper(self, lst, left, right):
while left < right:
lst[left], lst[right] = lst[right], lst[left]
left += 1
right -= 1
return lst