It's a good solution. On Sat, May 2, 2020, 00:52 Roelof Wobben via Pharo-users < pharo-users@lists.pharo.org> wrote:
> Op 1-5-2020 om 08:35 schreef Roelof Wobben: > > Op 1-5-2020 om 02:51 schreef Richard O'Keefe: > >> (oddSum + evenSum) dividedBy: 10 > >> > >> You previously had _ isDivisibleBy: 10 > >> which certainly works. > >> > >> Squeak, Pharo, and ST/X have #isDivisibleBy: > >> VisualWorks. Dolphin, and GNU Smalltalk do not. > >> > >> Here's the code from Number.st in ST/X. > >> isDivisibleBy:aNumber > >> "return true, if the receiver can be divided by the argument, > >> aNumber without a remainder. > >> Notice, that the result is only worth trusting, if the receiver > >> is an integer." > >> > >> aNumber = 0 ifTrue: [^ false]. > >> aNumber isInteger ifFalse: [^ false]. > >> ^ (self \\ aNumber) = 0 > >> > >> The comment is wrong: the question makes sense for any combination > >> of exact numbers. > >> When, as in this case, aNumber is a literal integer, all > >> #isDivisibleBy: really adds is overhead. > >> > >> (oddSum + evenSum) \\ 10 = 0 > >> > >> is quite clear, and completely portable. > >> > >> > >> > >> On Fri, 1 May 2020 at 02:16, Roelof Wobben <r.wob...@home.nl> wrote: > >>> Op 30-4-2020 om 16:06 schreef Richard O'Keefe: > >>>> This sounds very much like the Luhn test task at RosettaCode. > >>>> https://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers > >>>> except that there it is described as working on the digits of an > >>>> integer. > >>>> > >>>> (1) There are two approaches to traversing a sequence in reverse. > >>>> (A) Reverse the sequence, then traverse the copy forward. > >>>> aString reverse do: [:each | ...] > >>>> (B) Just traverse the sequence in reverse > >>>> aString reverseDo: [:each | ...] > >>>> My taste is for the second. > >>>> > >>>> (2) There are two approaches to deleting spaces. > >>>> (A) Make a copy of the string without spaces. > >>>> x := aString reject: [:each | each = Character space]. > >>>> x do: ... > >>>> (B) Ignore spaces as you go: > >>>> (i) aString do: [:each | each = Character space ifFalse: > >>>> [...]] > >>>> (ii) aString select: [:each | each ~= Character space] > >>>> thenDo: > >>>> [:each | ...] > >>>> > >>>> Combining (1A) and (2A) you get very obvious code: > >>>> (aString reject: [:each | each = Character space]) reverse do: > >>>> [:digit } ...] > >>>> Combining (1B) and (2Bi) you get more efficient code: > >>>> aString reverseDo: [:digit | > >>>> digit = Character space ifFalse: [ ...]] > >>>> > >>>> By the way, let's start by checking that the character in the > >>>> string *are* > >>>> digits or spaces: > >>>> (aString allSatisfy: [:each | each isDigit or: [each = > >>>> Character s[ace]]) > >>>> ifFalse: [^false], > >>>> > >>>> (3) There are two approaches to doubling the even digits. > >>>> (A) Make a new string that starts as a copy and change every > >>>> second > >>>> digit from the right. > >>>> (B) Simply *act* as if this has been done; keep track of > >>>> whether the > >>>> current digit position is even or odd and multiply by 1 > >>>> or 2 as > >>>> appropriate. > >>>> nextIsOdd := true. > >>>> aString reverseDo: [:digit | > >>>> digit = Character space ifFalse: [ > >>>> nextIsOdd > >>>> ifTrue: [oddSum := ...] > >>>> ifFalse: [evenSum := ...]. > >>>> nextIsOdd := nextIsOdd not]]. > >>>> > >>>> I *like* code that traverses a data structure exactly once and > >>>> allocates no intermediate garbage, so I'd be making (B) choices. > >>>> > >>>> > >>> For me , I use this to practice solving problems and doing the > >>> "right" > >>> steps. > >>> So I love it , that so many people share there way of solving it. > >>> I can learn a lot from it > >>> Expecially when they explain there thinking process so detailed. > >>> > >>> I like this code also a lot. > >>> Am I correct for testing if it is a valid string by doing this ^ > >>> (oddSum + evenSum) dividedBy: 10 > >>> > >>> Roelof > >>> > > > > > > oke, > > > > so this is better > > > > cardNumber := '8273 1232 7352 0569'. > > oddSum := 0. > > evenSum := 0. > > nextIsOdd := false. > > cardNumber reverseDo: [:character | > > digit := character digitValue. > > character = Character space ifFalse: [ > > nextIsOdd > > ifFalse: [oddSum := oddSum + digit ] > > ifTrue: [(digit >= 5 ) > > ifTrue: [evenSum := evenSum + (digit * 2) - 9 ] > > ifFalse: [ evenSum := evenSum + (digit * 2) ]]. > > nextIsOdd := nextIsOdd not]]. > > ^ evenSum + oddSum // 10 == 0. > > > > > > where I could even make a seperate method of the ifTrue branch when > > the digit is greater then 5. > > > > > nobody who can say if this is a good solution ? > > Roelof > >
