Rhyming scheme equivalence
Roses are red A
Violets are blue B
Sugar is sweet C
And so are you B
English teachers like to represent the rhyming pattern of poems with letters. Each line rhymes with lines with the same letter. In this case, B lines rhyme together, but the A and C lines don't rhyme. We will call that a "ABCB" rhyming scheme. However, the choice of letters is arbitrary. We could have called it "IBPB" or "XALA".
We want a way to know if two rhyming schemes are equivalent. Write a function that returns nil if they are not equivalent and returns a map of replacements if they are equivalent.
Examples
(equiv? "ABCB" "XALA") ;=> {\A \X \B \A \C \L}
(equiv? "A" "A") ;=> {}
(equiv? "A" "B") ;=> {\A \B}
(equiv? "AB" "A") ;=> nil
(equiv? "ABB" "XXY") ;=> nil
Thanks to this site for the problem idea, where it is rated Very Hard in Java. The problem has been modified.
Please submit your solutions as comments on this gist.
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