Python程序反转给定字符串中的单词

示例：让输入字符串为“我非常喜欢这个程序”。该函数应将字符串更改为“much very program this like i”

例子：

Input: s = “geeks quiz practice code” 
Output: s = “code practice quiz geeks”

Input: s = “getting good at coding needs a lot of practice” 
Output: s = “practice of lot a needs coding at good getting”

算法：

• 最初，将给定字符串的单个单词逐个反转，对于上面的示例，在反转单个单词之后，字符串应该是“i ekil siht margorp yrev hcum”。
• 在上面的示例中，从头到尾反转整个字符串以获得所需的输出“much very program this like i”。

下面是上述方法的实现：

Python3

# Python3 program to reverse a string
  
# Function to reverse each word in 
# the string
def reverse_word(s, start, end):
    while start < end:
        s[start], s[end] = s[end], s[start]
        start = start + 1
        end -= 1
  
s = "i like this program very much"
  
# Convert string to list to use it as 
# a char array
s = list(s)
start = 0
while True:
      
    # We use a try catch block because for
    # the last word the list.index() function
    # returns a ValueError as it cannot find 
    # a space in the list
    try:
        # Find the next space
        end = s.index(' ', start)
  
        # Call reverse_word function
        # to reverse each word
        reverse_word(s, start, end - 1)
  
        #Update start variable
        start = end + 1
  
    except ValueError:
  
        # Reverse the last word
        reverse_word(s, start, len(s) - 1)
        break
  
# Reverse the entire list
s.reverse()
  
# Convert the list back to
# string using string.join() function
s = "".join(s)
  
print(s)
  
# This code is contributed by Prem Nagdeo

输出：

much very program this like i

另一种方法：

我们可以通过以相反的方式拆分和保存字符串来完成上述任务。

下面是上述方法的实现：

Python3

# Python3 program to reverse a string
# s = input()
s = "i like this program very much"
words = s.split(' ')
string =[]
for word in words:
    string.insert(0, word)
  
print("Reversed String:")
print(" ".join(string))
  
# Solution proposed bu Uttam

输出：

Reversed String:
much very program this like i

时间复杂度： O(n)

不使用任何额外空间：
上面的任务也可以通过从中间开始拆分和直接交换字符串来完成。由于涉及直接交换，因此消耗的空间也更少。

下面是上述方法的实现：

Python3

# Python3 code to reverse a string
  
# Reverse the string
def RevString(s,l):
    
  # Check if number of words is even
  if l%2 == 0:
      
    # Find the middle word
    j = int(l/2)
      
    # Starting from the middle 
    # start swapping words
    # at jth position and l-1-j position
    while(j <= l - 1):
      s[j], s[l - j - 1] = s[l - j - 1], s[j]
      j += 1
        
  # Check if number of words is odd
  else:
      
    # Find the middle word
    j = int(l/2 + 1)
      
    # Starting from the middle 
    # start swapping the words
    # at jth position and l-1-j position
    while(j <= l - 1):
      s[j], s[l - 1 - j] = s[l - j - 1], s[j]
      j += 1
      
    # return the reversed sentence
    return s;
        
# Driver Code
s = 'getting good at coding needs a lot of practice'
string = s.split(' ')
string = RevString(string,len(string))
print(" ".join(string))

输出：

practice of lot a needs coding at good getting

有关详细信息，请参阅有关给定字符串中的反向单词的完整文章！