RE: eve/did=.talktalktalk... - haskell is just as good

RE: http://ozgurakgun.blogspot.com/2010/04/evedidtalktalktalk.html

If you implement a simple algorithm usings haskell's list comprehensions, the performance turns out to be just as good. Of course the tools mentioned in the previous post are a) general purpose tools, b) would be far better in harder problems.

Anyway, the interesting part of the haskell code is the following:

evedidtalk =
    [
        [e,v,d,i,t,a,l,k] |
        e <- [1..9],
        v <- [0..9] \\ [e],
        d <- [1..9] \\ [e,v],
        i <- [0..9] \\ [e,v,d],
        t <- [0..9] \\ [e,v,d,i],
        a <- [0..9] \\ [e,v,d,i,t],
        l <- [0..9] \\ [e,v,d,i,t,a],
        k <- [0..9] \\ [e,v,d,i,t,a,l],
        digitsToInt [e,v,e] * 9999 ==
        digitsToInt [d,i,d] * digitsToInt [t,a,l,k]
    ]

Here, evedidtalk is a list of digits, that satisfy the only constraint we have. The key to performance is limiting the number of alternatives generated using the \\ (list difference) operator.
A poor-in-performance alternative would be generating all possibilities and then checking for the second constraint we had, the alldiff.

Compiled with -O2 using ghc, this finds the two possible solutions in under a second (yet, slightly slower than tailor+minion).