[Haskell-cafe] Re: Solving a geometry problem with Haskell

Achim Schneider wrote:

Achim Schneider wrote:

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"Rafael Almeida" wrote:

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perfectSquares :: [Integer] perfectSquares = zipWith (*) [1..] [1..]

...

isPerfectSquare :: Integer -> Bool isPerfectSquare x = (head $ dropWhile (

what about

module Main where

isPerfectSquare :: Integer -> Bool isPerfectSquare n = sqrrt == fromIntegral (truncate sqrrt) where sqrrt = sqrt $ fromIntegral n

? It's a hell alot faster, but I have no idea if some numerical property of square roots could make it give different results than your version, in rare cases.

Well, even if so, I bet calculating the square root by successive approximation using integers would still be faster, it's O(ld(n)) instead of O(n).

(and you can use a truncated sqrt as initial guess) This may seem like cheating, but then I'm a game programmer... -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.