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Talk:Sum and product puzzle

From Rosetta Code

Remove draft status?[edit]

Now that I improved the task description, is this task ready for prime time? --Smls (talk) 14:47, 5 August 2016 (UTC)

I went ahead and took it out of draft status. --Smls (talk) 12:35, 20 August 2016 (UTC)

Scala[edit]

Could someone in the know please explain these two lines in plain English?

val step2 = step0 filter { sumEq(_) forall { prodEq(_).size != 1 }}

  step2 contains the pairs whose product is unique and ??
 

val step3 = step2 filter { prodEq(_).intersect(step2).size == 1 }

step2 filters the step0 integer pairs for pairs where "For every possible sum decomposition of the number X+Y, the product has in turn more than one product decomposition"
step3 filters the set defined by step2 for pairs where "The number X*Y has only one product decomposition for which fact 1 is true"
Perhaps the Haskell or JavaScript versions might seem more legible ? Hout (talk) 17:35, 21 October 2016 (UTC)
Still not explicit enough :-( Sorry Meanwhile I added 2 translations where I could understand the source (AWK and GO/ --Walterpachl (talk) 18:54, 26 October 2016 (UTC)
Do higher order functions feature in the architecture or traditions of REXX ? If not, the patterns of functional composition used in the Haskell and Scala etc examples may be a little hard to translate all that directly. Hout (talk) 19:18, 3 November 2016 (UTC)

A question on GO[edit]

I translated GO to Rexx and the "final" piece missing for understanding is this:

Why does this justify the removal of the pair p??

Shouldn't the pair a/b be discarded???

for a := 2; a < s/2+s&1; a++ {
   b := s - a
   if products[a*b] == 1 {
   // Excluded because P would have a unique product
   continue pairs

--Walterpachl (talk) 19:59, 05 November 2016 (UTC)

I think I found the answer myself:-) If ANY of the decompositions of the given pair's sum had a unique product I couldn't be sure that P does NOT know. So all pairs resulting in the given sum could be eliminated not just the one at hand. (They will be later on or have already been...) --Walterpachl (talk) 05:59, 10 November 2016 (UTC)

Java program inconsistent with others[edit]

It allows the sum to be equal to maximum value. The threshold for a second solution should be X+Y<1866, not 1865.