Problem Statement

A semordnilap is a word (or phrase) that spells a different word (or phrase) backward. "Semordnilap" is a word that itself is a semordnilap. Example: lager and regal

This task does not consider semordnilap phrases, only single words. Using only words from this list, report the total number of unique semordnilap pairs, and print 5 examples. Two matching semordnilaps, such as lager and regal, should be counted as one unique pair. (Note that the word "semordnilap" is not in the above dictionary.)

Let's start with the solution:

   isSemordnilap=: |.&.> (~: *. e.) ]
   unixdict=: <;._2 freads 'unixdict.txt'
   #semordnilaps=: ~. /:~"1 (,. |.&.>) (#~ isSemordnilap) unixdict
158


   (5?.158) { semordnilaps
┌────┬────┐
│kay │yak │
├────┼────┤
│nat │tan │
├────┼────┤
│avis│siva│
├────┼────┤
│flow│wolf│
├────┼────┤
│caw │wac │
└────┴────┘