How to append and join the center element(when occuring more than once) in a palindrome

Question

I want to make a palindrome lexicographically from a user input string

I take the input string and count each alphabet's occurrence(odd or even) and store them accordingly in a dictionary. Then, I find the centre element and also store the left and right parts in a sorted manner.

Now, how do I continue when the centre element has multiple occurrences?

from collections import Counter
even={}
odd={}
s=input()
s=list(s)
s.sort()
s=Counter(s)
for i,j in s.items():
    if j%2==0:
        even.update({i:j})
    else:
        odd.update({i:j})
print(even,odd)        

od=list(odd)   
ev=list(even)

if len(odd)==1:
    center=od[0]
elif len(odd)>1:
    print('Not Possible')
elif len(odd)==0:
    center=''

right=[]

for i,j in even.items():
    right.append(i*int(j/2))

print(right)         
left=right[::-1]
print(left)

pal=right+list(center)+left

palin=''.join(pal)
print(palin)

For example, when the input is crocorc, Output should be corcroc, But I am stuck at orcrc.

Answer 1

You can check for multiple occurrences of centre element, and add the extra elements in the even list:

if odd[od[0]] > 1:
    even[od[0]] = odd[od[0]] - 1

We do a -1 because we have to use one element as the centre element. Now the issue will be that even will not be sorted so you need to sort it.

even = sorted(even.items(), key=lambda kv: kv[0])
import collections
even = collections.OrderedDict(even)

First line of code above sorts even which returns a list of tuples, and third line converts it back to dictionary.

Here is the finished code

from collections import Counter
even={}
odd={}
s=input()
s=list(s)
s.sort()
s=Counter(s)
for i,j in s.items():
    if j%2==0:
        even.update({i:j})
    else:
        odd.update({i:j})
print(even,odd)        

od=list(odd)   
ev=list(even)

if len(odd)==1:
    center=od[0]
elif len(odd)>1:
    print('Not Possible')
elif len(odd)==0:
    center=''

if odd[od[0]] > 1:
    even[od[0]] = odd[od[0]] - 1

right=[]

even = sorted(even.items(), key=lambda kv: kv[0])
import collections
even = collections.OrderedDict(even)

for i,j in even.items():
    right.append(i*int(j/2))

print(right)         
left=right[::-1]
print(left)

pal=right+list(center)+left

palin=''.join(pal)
print(palin)