Longest palindromic substrings

Longest palindromic substrings is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Let given a string s. The goal is to find the longest palindromic substring in s.

REXX

<lang rexx>/*REXX program finds and displays the longest palindromic string(s) in a given string. */ parse arg s . /*obtain optional argument from the CL.*/ if s== | s=="," then s= 'babaccd' /*Not specified? Then use the default.*/ L= length(s) /*obtain length of the specified string*/ longest= 0 /*longest palindrome found (so far). */ @.= /*initialize all possible lists to null*/

          do j=1   for L                        /*search for palindromes in the string.*/
            do k=j  to L;      LL= k - j + 1    /*obtain length of possible palindromes.*/
            if LL<longest      then iterate     /*Palindrome length<max?  Then skip it.*/
            $= substr(s, j, LL)                 /*obtain a possible palindromic substr.*/
            if $\==reverse($)  then iterate     /*Not a palindrome?       Then skip it.*/
            longest= max(longest, LL)           /*set the longest palindrome to this L.*/
            @.LL= @.LL $                        /*add a palindromic substring to a list*/
            end   /*k*/
          end     /*j*/

if longest==0 then do; say 'no longest palindromic string was found for: ' s; exit 13

                   end

say ' longest palindromic substrings for string: ' s /*show title.*/ say '────────────────────────────────────────────'copies('─', 2+length(s)) /*show sep. */

 do n=1  for words(@.longest)                   /*show longest palindromic substrings. */
             /*show pals. */
 say '    (length='longest")   "   word(@.longest, n)
 end   /*n*/                                    /*stick a fork in it,  we're all done. */</lang>

output   when using the default input:

 longest palindromic substrings for string:  babaccd
─────────────────────────────────────────────────────
    (length=3)    bab
    (length=3)    aba

Ring

<lang ring> load "stdlib.ring"

st = "babaccd" palList = []

for n = 1 to len(st)-1

   for m = n+1 to len(st)
       sub = substr(st,n,m-n)
       if ispalindrome(sub) and len(sub) > 1
          add(palList,[sub,len(sub)])
       ok
   next

next

palList = sort(palList,2) palList = reverse(palList) resList = [] add(resList,palList[1][1])

for n = 2 to len(palList)

   if palList[1][2] = palList[n][2]
      add(resList,palList[n][1])
   ok

next

see "Input: " + st + nl see "Longest palindromic substrings:" + nl see resList </lang>

Output:

Input: babaccd
Longest palindromic substrings:
bab
aba