CODEWITHSUNDEEP
python
Mr. Green
Mr. Green

Reputation: 49

How to increment and decrement with a string Python?

Hope you all are doing well in these times.

here's my code:


def ab(n):


    first = 0
    last = -1 

    endprod = n[first] + n[last]
    endprod2 = n[first+1] + n[last-1]
    endprod3 = n[first+2] + n[last-2]
    endprod4 = n[first+3] + n[last-3]
    endprod5 = n[first+4] + n[last-4]

        
    endprod100 = endprod[::-1] + endprod2[::-1] + endprod3[::-1]+ endprod4[::-1]+ endprod5[::-1]

    return endprod100

I was able do to it, however mine isn't a loop. Is there a way to convert my code into a for loop. So, increment by 1 and decrement by 1.

Thanks,

Upvotes: 2

Views: 370

Answers (4)

Swifty
Swifty

Reputation: 3409

You could also recurse it:

def ab(s):
    if len(s)>2:
        return s[-1]+s[0]+ab(s[1:-1])
    else:
        return s

But the last part of Riccardo's answer fits your question more closely.

Upvotes: 1

Savir
Savir

Reputation: 18418

There are already a lot of good answers that are probably clearer, easier to read and much better suited for learning purposes than what I'm about to write. BUT... something I wanted to bring up (maybe just telling myself, because I tend to forget it) is that sometimes destroying the original argument can facilitate this sort of things.

In this case, you could keep "poping" left and right, shrinking your string until you exhaust it

def swap_destr(my_str):
    result = ""
    while len(my_str) > 1:
        result += my_str[-1]  # Last char
        result += my_str[0]   # First char
        my_str = my_str[1:-1] # Shrink it!
    return result + my_str  # + my_str just in case there 1 char left

print(swap_destr("0123456789"))
print(swap_destr("123456789"))

# Outputs:
# 9081726354
# 918273645

This is also a good problem to see (and play with) recursion:

def swap_recur(my_str):
    if len(my_str) <= 1:
        return my_str
    return my_str[-1] + my_str[0] + swap_recur(my_str[1:-1])

print(swap_recur("0123456789"))
print(swap_recur("123456789"))

# Outputs:
# 9081726354
# 918273645

Upvotes: 0

amirhm
amirhm

Reputation: 1249

you need to split your string for your loop, means first you broke your string to half then build your string, you could use zip to iterate over multiple iteratable. something like this:

def ab(s):
    out = ""
    for v0,v1 in zip(s[:len(s)//2 -1 :-1], s[:len(s)//2 ]):
        out += v0 + v1
    return out

the better version you should write without loop. like this:

out = "".join(map(lambda x: "".join(x), zip(s[:len(s)//2 -1 :-1], s[:len(s)//2 ])))

Upvotes: 0

Riccardo Bucco
Riccardo Bucco

Reputation: 15364

Try this:

def ab(n):
    result = ''
    for j in range(len(n) // 2):
        result += n[-j-1] + n[j]
    if len(n) % 2 == 1:
        result += n[len(n) // 2]
    return result

You also need the part

if len(n) % 2 == 1:
    result += n[len(n) // 2]

because your input string might have an odd number of characters

Examples:

>>> ab('0123456789')
'9081726354'
>>> ab('01234956789')
'90817263549'

If you want to reuse your original logic:

def ab(n):
    result = ''
    first = 0
    last = -1
    for j in range(len(n) // 2):
        result += n[last-j] + n[first+j]
    if len(n) % 2 == 1:
        result += n[len(n) // 2]
    return result

Upvotes: 1

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