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Find longest palindrome formed by removing or shuffling chars from string in Python
Suppose we have a string; we have to find the longest palindrome that can be generated by deleting or shuffling the characters from the string. And if there are more than one palindrome then return only one.
So, if the input is like pqqprrs, then the output will be pqrsrqp.
To solve this, we will follow these steps −
count := array of size 256, filled with 0
for i in range 0 to size of string, do
count[ASCII of(string[i]) ] := count[ASCII of(string[i]) ] + 1
begin := blank string, mid := blank string, end := blank string
character := ASCII of('a')
while character <= ASCII of('z') , do
if count[character] AND 1 is non-zero, then
mid := character
count[character] := count[character] - 1
character := character - 1
otherwise,
for i in range 0 to count[character]/2 (integer division), do
begin := begin + character from (character)
character := character + 1
end := begin
end := reverse end
return begin concatenate character from (mid) concatenate end
Example
Let us see the following implementation to get better understanding −
def get_palindrome(string):
count = [0]*256
for i in range(len(string)):
count[ord(string[i])] += 1
begin = ""
mid = ""
end = ""
character = ord('a')
while character <= ord('z'):
if (count[character] & 1):
mid = character
count[character] -= 1
character -= 1
else:
for i in range(count[character]//2):
begin += chr(character)
character += 1
end = begin
end = end[::-1]
return begin + chr(mid) + end
string = "pqqprrs"
print(get_palindrome(string))Input
"pqqprrs"
Output
pqrsrqp
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