Re: [Bug-apl] Best way to solve my daughter's maths problem

[enztec]

On Wed, 25 Jan 2017 19:23:50 -0700
address@hidden wrote:

> 
> This is the full brute force method  - basically a permutation of op chars 
> (luckily apl has ⍎)
> 
> ∇top4
>  op←'-+×÷'
>  top←op[(1 1 1 1), 1+4 4 4 4⊤⍳255]
>  op1←256 1⍴top[1;]
>  op2←256 1⍴top[2;]
>  op3←256 1⍴top[3;]
>  op4←256 1⍴top[4;]
>  ttop←(256 4⍴'(((4'),op1,(256 2⍴'4)'),op2,(256 2⍴'4)'),op3,(256 
> 2⍴'4)'),op4,'4'
>  aa←1
>  a: ' ' ◊ ⍞←aa,' ',⍎ttop[aa;]
>  ⍝ ⍎(7 = ⍎ttop[aa;])/'⍞←'' '',yes'
>  ⍎(7 = ⍎ttop[aa;])/'⍞←'' '',ttop[aa;]'
>  →(256aa←aa+1)/a                                                       there 
> is a missing 'greater then equal'  >=  (in pascal) between the 256 >= aa     
> seems to have been stripped out somewhere?
> ∇
> 
> 
> On Wed, 25 Jan 2017 10:38:58 +0800
> Elias Mårtenson <address@hidden> wrote:
> 
> > But that's what my solution did. The problem is that that solution doesn't
> > evaluate things like (4+4)×(4+4)-4
> > 
> > Regards,
> > Elias
> > 
> > On 25 January 2017 at 09:49, <address@hidden> wrote:
> > 
> > >
> > > op ← '+-x÷'
> > >
> > > i meant a brute force     creating a HUGE matrix       '(((4 op[⍳4] 4)
> > > op[⍳4] 4) op[⍳4] 4) op[⍳4] 4'
> > >
> > >
> > >
> > >
> > >
> > > On Wed, 25 Jan 2017 08:49:37 +0800
> > > Elias Mårtenson <address@hidden> wrote:
> > >
> > > > Thanks, but the code I included already gives me that solution, so that
> > > was
> > > > never the problem.
> > > >
> > > > The issue here is more one of trying to come up with a good APL
> > > solution. I
> > > > really don't like mine, it's too verbose.
> > > >
> > > > Regards,
> > > > Elias
> > > >
> > > > On 25 Jan 2017 8:46 AM, <address@hidden> wrote:
> > > >
> > > > > since no one has responded yet this is my best guess without pure
> > > random
> > > > > code testing from array of chars following your rules
> > > > >
> > > > > the answer is :  ⍎'(((4+4)x4)-4)÷4'     ;)
> > > > > i think the problem is from an episode of cartalk ??
> > > > >
> > > > >
> > > > >
> > > > > On Tue, 24 Jan 2017 23:47:10 +0800
> > > > > Elias Mårtenson <address@hidden> wrote:
> > > > >
> > > > > > My daughter had this maths problem, and quote it from memory:
> > > > > >
> > > > > > Given five 4's, separated by the mathematical functions +, -, × and 
> > > > > > ÷
> > > > > form
> > > > > > the number 7. The problem also allowed her to use parentheses.
> > > > > >
> > > > > > I decided to write an APL expression to solve this, and this is what
> > > I
> > > > > came
> > > > > > up with:
> > > > > >
> > > > > >
> > > > > > *    d ← {⍵÷⍺}*
> > > > > > *    (↑¨ 7 = ⍎¨ v) / v ← {"4 " , ↑,/ {{⍵," 4 "}¨⍵} ⍵}¨ ,↑∘.,/4 ⍴
> > > ⊂'+-×d'*
> > > > > >
> > > > > > Now, this program finds two solutions, which is good enough for me.
> > > > > > However, my program doesn't find solutions that require parentheses.
> > > > > >
> > > > > > Problem 1: Can anyone simplify my program?
> > > > > > Problem 2: Can anyone come up with a solution that also checks for
> > > > > > parentheses?
> > > > > >
> > > > > > Regards,
> > > > > > Elias
> > > > >
> > > > >
> > >
> > >
>