I did not ask why you were validating input.
I asked about why you *repeatedly* validated input.
Think of it this way:
publicMethod: arg1 also: arg2
... check arg1 ...
... check arg2 ...
^self privateMethod: arg1 also: arg2
privateMethod: arg1 also: arg2
... trust that arg1 and arg2 are valide ...
... recursive calls use #privateMethod:andAlso: ...
... not #publicMethod:andAlso: and must ensure ...
... that arguments are valid by construction ...
In my solution to the "Grains" exercism, I have
atSquare: n -- checks its argument
total ^(1 bitShift: 64) - 1
You are required to implement these two methods, true.
You are NOT required to implement #total by calling #atSquare:.
Not even once. Nor is #atSquare: required to be recursive.
On Mon, 6 Jan 2020 at 02:05, Roelof Wobben <r.wob...@home.nl> wrote:
>
> Hello Ricard.
>
> You mean when I calcualate the total of a board.
> That is because on when I had to calculate the number of a particular
> field there were tests where the number was lower then zero or higher
> then 64 which makes no sense.
>
> But im open for a solution where on a particular field I could check for
> that and for the total I do not need that part.
>
> Roelof
>
>
>
> Op 5-1-2020 om 13:58 schreef Richard O'Keefe:
> > Time microsecondsToRun: [
> > |n|
> > n := (2 raisedToInteger: 8 * 8) - 1.
> > Transcript
> > nextPutAll: 'The number of grains on an 8x8 chessboard is ';
> > print: n; cr; endEntry].
> > <PRINT-IT>
> > On my laptop, this reports 194 microseconds.
> >
> > Why would you use recursion, anyway?
> >
> > Time microsecondsToRun: [
> > |n|
> > n := (1 to: 8 * 8) inject: 0 into: [:acc :each | acc+acc+1].
> > Transcript
> > nextPutAll: 'The number of grains on an 8x8 chessboard is ';
> > print: n; cr; endEntry].
> > <PRINT-IT>
> > On the same laptop, this reports 118 microseconds.
> >
> > One of the lessons of 'functional' languages, promptly adopted by
> > Smalltalk, is
> > to encapsulate control structures into reusable methods, such as
> > #inject:into:,
> > more commonly known as `foldl` in functional languages. It's then none of
> > my business whether such a method works by recursion, iteration, or gangs
> > of otherwise seasonally unemployed Christmas elves.
> >
> > In my own Smalltalk library,
> > (GeometricSeries new: 64 from: 1 byFactor: 2) sum
> > only takes 15 microseconds.
> >
> > I do note that you are calling validateInput repeatedly. Why?
> >
> >
> > On Sun, 5 Jan 2020 at 07:41, Roelof Wobben via Pharo-users
> > <pharo-users@lists.pharo.org> wrote:
> >> Oke,
> >>
> >> So I can better not use recursion for this problem if I understand you
> >> well, Richard.
> >>
> >> Roelof
> >>
> >>
> >>
> >> Op 4-1-2020 om 19:02 schreef Richard Sargent:
> >>
> >> On Sat, Jan 4, 2020 at 9:47 AM Roelof Wobben via Pharo-users
> >> <pharo-users@lists.pharo.org> wrote:
> >>> Hello,
> >>>
> >>> For a exercism challenge I need to calculate the total grains on a
> >>> chessboard.
> >>> So I did :
> >>>
> >>> atSquare: anInteger
> >>> self validateInput: anInteger.
> >>> ^ anInteger = 1
> >>> ifTrue: [ 1 ]
> >>> ifFalse: [ 2 * (self atSquare: anInteger - 1) ]
> >>>
> >>>
> >>> but when I run the tests , the vm seems to be not responsive for some 4
> >>> - 5 seconds.
> >>>
> >>> Is there a way I can use this code and take care that the vm stays
> >>> responsive.
> >>
> >> What do you want the VM to do in addition to calculating that sum while it
> >> is calculating that sum?
> >>
> >>
> >> The best way to keep the VM responsive is to take a page from Gauss'
> >> notebook and pay attention to the numbers[1]. Let's consider the first
> >> four squares and extrapolate from there.
> >>
> >> In binary, the squares hold the following grains: 2r1, 2r10, r2100, and
> >> 2r1000. When we add them up, we get 2r1111. If we use Gauss' tricks, we
> >> can notice that 2r1111 is equal to 2r10000 - 1. So, the sum of the grains
> >> on the first 4 squares is 2^5 - 1. You can easily generalize that pattern,
> >> of course. Then your program can calculate the answer quickly.
> >>
> >>
> >> [1] The story goes that Gauss' teacher was frustrated with his student's
> >> abilities and set him a challenge to occupy him for some time: sum the
> >> numbers from 1 through 100. Gauss immediately answered 5,050, much to his
> >> teacher's chagrin.
> >>
> >>> Regards,
> >>>
> >>> Roelof
> >>>
> >>>
>
