Question

以下代码尝试解决https://projecteuler.net/problem=87

import Math.NumberTheory.Primes.Sieve -- from package arithmoi

gen::[Integer]->Integer->[Integer]-- time complexity : n! , n = numberofprimes
gen pmlist limit=filter (\x->x<=limit) prelist
  where prelist=do
          let ls1=filter (\(x::Integer)->(x^2)<=limit) pmlist
          a<-ls1
          let ls2=filter (\(x::Integer)->(x^3)<=limit) ls1
          b<-ls2
          c<-filter (\(x::Integer)->(x^4)<=limit) ls2
  --  guard $ (b>=a)&&(c>=b)
          let res=(a^2+b^3+c^4)
          return res
main=do
  print "euler proj" -- other's answer:1097343 , my : 1139575

  print $ length  $ ep87 limit_1
--  print $  ep87

primesUnder i = takeWhile (\x->x<=i) primes -- library function
limit_1::Integer
limit_1=50000000
limit_2=1000000000
limit_3=10000000000

ep87 lmt =  gen (primesUnder lmt) lmt

另一个答案：1097343，但这段代码片段给出了1139575，可能是罪魁祸首？

Answer 1

您的方法会生成重复项：

ghci> ep87 150
[28,93,47,112,145,33,98,52,117,150,49,114,68,133,73,138,92,145]
              ^^^                                          ^^^

简单的素数挑战haskell代码给出了错误的答案

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