CODEWITHSUNDEEP
python
WouterB
WouterB

Reputation: 35

How do i invert every odd letter in a string?

So basically I have to make a code that inverts every odd letter of a string. I got a fair way, but couldn't figure out how to put the string back together properly.

So the output should be 'hlleo', but instead i get 'hloe'. How do i fix this? Input is hello
Expected output is hlleo
Output is hloe 

word = 'hello'
output = ''
value = -1
word1 = word[0::2]
word2 = word[1::2]
word2 = word2[::-1]
print(word2)
print(word1)
for letter in word2:
    value += 2
    output = word1[:value] + letter + word1[value:]
    print(output)
print('Correct output should be "hlleo"')

Upvotes: 0

Views: 257

Answers (5)

jpkotta
jpkotta

Reputation: 9437

def revodd(s):
    l = list(s)
    l[1::2] = reversed(l[1::2])
    return "".join(l)

Convert to a list of strings (because lists are mutable and strings aren't), set a slice of the odd indices to a reversed version of itself, and join the list back into a string. I see @schwobaseggl has done the reverse with a slice, but I think using reversed is much more readable.

Test cases:

In [23]: revodd("0123456789")
Out[23]: '0927456381'

In [24]: revodd("012345678")
Out[24]: '072543618'

In [25]: revodd("hello")
Out[25]: 'hlleo'

Upvotes: 0

Sam
Sam

Reputation: 514

Unless I have misunderstood your question, this can only 'work properly' with odd length strings so that the odd indexed characters are all swapping with other odd indexed characters. 

def invert_odds(string):

    # Get reverse of string
    reverse = string[::-1]

    new_string = ""

    # Make new string with chars from either original or reversed
    # strings depending on index
    for i in range(len(string)):
        if i % 2 == 0:
            new_string += string[i]
        else:
            new_string += reverse[i]

    return new_string

Upvotes: 0

pault
pault

Reputation: 43534

Here's a one liner.

inv_word = "".join([word[i] if i%2==0 else word[len(word)-(i+1)] for i in range(len(word))])

The logic here is that we build a new list of characters by iterating over the word. If the index is even (i%2==0), then we use the corresponding index in the word. Otherwise, we use the inverted character which is found at index len(word)-(i+1).

At the end, join the list together with "".join() to make it a string.

Upvotes: 0

user2390182
user2390182

Reputation: 73480

You can turn the string into a list and use slice assignment and join it back together:

w = 'abcdef'
l = list(w)
l[1::2] = l[1::2][::-1]
w2 = ''.join(l)
# 'afcdeb'

Upvotes: 0

Amit Tripathi
Amit Tripathi

Reputation: 7261

This works:

In [6]: word = 'hello'

In [7]: dorw = list(reversed(word))

In [8]: new_word = ''

In [9]: for i in range(len(word)):
   ...:     w = word[i]
   ...:     if i % 2 != 0:
   ...:         w = dorw[i]
   ...:     new_word += w
   ...:

In [10]: new_word
Out[10]: 'hlleo'

Based on index i a word is taken either from the real "word" or the reversed version of it.

Upvotes: 2

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