Why do I not get the correct answer for Euler 56 in J?

Posted by Gregory Higley on Stack Overflow See other posts from Stack Overflow or by Gregory Higley
Published on 2010-06-15T07:47:52Z Indexed on 2010/06/15 7:52 UTC
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beginner

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project-euler

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tacit-programming

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j

I've solved 84 of the Project Euler problems, mostly in Haskell. I am now going back and trying to solve in J some of those I already solved in Haskell, as an exercise in learning J.

Currently, I am trying to solve Problem 56. Let me stress that I already know what the right answer is, since I've already solved it in Haskell. It's a very easy, trivial problem. I will not give the answer here.

Here is my solution in J:

digits =: ("."0)":"0
eachDigit =: adverb : 'u@:digits"0' NB. I use this so often I made it an adverb.
cartesian =: adverb : '((#~ #) u ($~ ([:*~#)))'
>./ +/ eachDigit x: ^ cartesian >: i. 99

This produces a number less than the desired result. In other words, it's wrong somehow. Any J-ers out there know why? I'm baffled, since it's pretty straightforward and totally brute force.

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