推 sophialiege :enumerate some small cases 08/26 06:22
let Σ = {a,b,c,d}. A palindrome over Σ is a (possibly empty) sequence of
symbols from Σ such that the sequence is the same as its reverse listing.
So, for example, aba is a palindrome (of length 3) while aacb is not.
Now let S(n), n>=0, denote the number of palindromes over Σ of length n
drive a recurrence relation for S(n) for n>=2
請問這要怎麼導呢?
謝謝
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