```On 4/9/07, Raj Sahae <rajsahae / gmail.com> wrote:
> Christian Neukirchen wrote:
> > =begin
> >
> >> The quiz, then, is to solve this problem without thinking, instead
> >> letting the computer think for you.
> >>
> >
> > I did not intent to seriously submit this solution, but it can be
> > helpful as an example of how to use Ruby to solve a problem quickly
> > without thinking too much or locating Knuth on the bookshelve.
> > Writing this code took maybe ten minutes and happened step-by-step
> > with checking the immediate results.
> >
> > Since there are only 168 solutions (254 if you allow a sign before the
> > first digit), brute-forcing is the simplest thing one can do.
> > Additional operations can be added by changing the base and mapping
> > the digits onto further operations.  (Different digit order is not
> > that easy to implement and maybe be futile to do with brute-forcing.)
> > =end
> >
> > (00000000..'22222222'.to_i(3)).map { |x| x.to_s(3).rjust(8, "0").
> >                                                    tr('012', '-+ ') }.
> >   find_all { |x| x.count("-") == 2 and x.count("+") == 1 }.
> >   map { |x|
> >     t = "1" + x.split(//).zip((2..9).to_a).join.delete(" ")
> >     [eval(t), t]
> >   }.sort.each { |s, x|
> >     puts "*****************" if s == 100
> >     puts "#{x}: #{s}"
> >     puts "*****************" if s == 100
> >   }
> >
> > __END__
> >
> > 2#787<p4>lilith:~/mess/current\$ ruby quiz119.rb |grep -C4 100\$
> > 123-456-7+89: -251
> > 123+45-67-89: 12
> > 123-45+67-89: 56
> > *****************
> > 123-45-67+89: 100
> > *****************
> > 12+345-67-89: 201
> > 1-234+567-89: 245
> > 1-23-456+789: 311
> >
> >
> I'm sorry to be a noob on this, but can someone please explain to me
> what this is doing.  If it works, it must be genius, and I can't figure
> it out.
>
> Raj Sahae
>
>
Actually I have no idea whatsoever, this is normally a good starting point ;)
irb is our friend of course, so let us hack away:
irb(main):003:0> (000..'222'.to_i(3)).map{|x|x.to_s(3).rjust(3,
"0").tr('012', '-+ ')}
=> ["---", "--+", "-- ", "-+-", "-++", "-+ ", "- -", "- +", "-  ",
"+--", "+-+", "+- ", "++-", "+++", "++ ", "+ -", "+ +", "+  ", " --",
" -+", " - ", " +-", " ++", " + ", "  -", "  +", "   "]

Aha the ternary array is used to create all kind of operator
combinations including " ".
I do not know exactly what this is good for right now, but I guess we
will learn.
As a next step I increase 3 to 8 as I think we can understand that now
and I will add the next method
(00000000..'22222222'.to_i(3)).map { |x| x.to_s(3).rjust(8,
"0").tr('012', '-+ ') }.find_all { |x| x.count("-") == 2 and
x.count("+") == 1 }
=> ["--+     ", "-- +    ", "--  +   ", "--   +  ", "--    + ", "--
+", "-+-     ", "-+ -    ", "-+  -   ", "-+   -  ", "-+    - ", "-+
-", "- -+    ", "- - +   ", "- -  +  ", "- -   + ", "- -    +", "-
+-    ", "- + -   ", "- +  -  ", "- +   - ", "- +    -", "-  -+   ",
"-  - +  ", "-  -  + ", "-  -   +", "-  +-   ", "-  + -  ", "-  +  -
", "-  +   -", "-   -+  ", "-   - + ", "-   -  +", "-   +-  ", "-   +
- ", "-   +  -", "-    -+ ", "-    - +", "-    +- ", "-    + -", "-
-+", "-     +-", "+--     ", "+- -    ", "+-  -   ", "+-   -  ", "+-
- ", "+-     -", "+ --    ", "+ - -   ", "+ -  -  ", "+ -   - ", "+
-    -", "+  --   ", "+  - -  ", "+  -  - ", "+  -   -", "+   --  ",
"+   - - ", "+   -  -", "+    -- ", "+    - -", "+     --", " --+
", " -- +   ", " --  +  ", " --   + ", " --    +", " -+-    ", " -+ -
", " -+  -  ", " -+   - ", " -+    -", " - -+   ", " - - +  ", " - -
+ ", " - -   +", " - +-   ", " - + -  ", " - +  - ", " - +   -", " -
-+  ", " -  - + ", " -  -  +", " -  +-  ", " -  + - ", " -  +  -", " -
-+ ", " -   - +", " -   +- ", " -   + -", " -    -+", " -    +-", "
+--    ", " +- -   ", " +-  -  ", " +-   - ", " +-    -", " + --   ",
" + - -  ", " + -  - ", " + -   -", " +  --  ", " +  - - ", " +  -
-", " +   -- ", " +   - -", " +    --", "  --+   ", "  -- +  ", "  --
+ ", "  --   +", "  -+-   ", "  -+ -  ", "  -+  - ", "  -+   -", "  -
-+  ", "  - - + ", "  - -  +", "  - +-  ", "  - + - ", "  - +  -", "
-  -+ ", "  -  - +", "  -  +- ", "  -  + -", "  -   -+", "  -   +-", "
+--   ", "  +- -  ", "  +-  - ", "  +-   -", "  + --  ", "  + - - ",
"  + -  -", "  +  -- ", "  +  - -", "  +   --", "   --+  ", "   -- +
", "   --  +", "   -+-  ", "   -+ - ", "   -+  -", "   - -+ ", "   - -
+", "   - +- ", "   - + -", "   -  -+", "   -  +-", "   +--  ", "   +-
- ", "   +-  -", "   + -- ", "   + - -", "   +  --", "    --+ ", "
-- +", "    -+- ", "    -+ -", "    - -+", "    - +-", "    +-- ", "
+- -", "    + --", "     --+", "     -+-", "     +--"]

It is a little longer but we see already that only 2 minuses and 1
plus is allowed...
By storing this into a variable tmp we can continue easily to explore
what is happening
tmp.map{|x|  t = "1" + x.split(//).zip((2..9).to_a).join.delete(" ") ;
[eval(t),t]}
=> [[456785, "1-2-3+456789"], [56754, "1-2-34+56789"], [6443,
"1-2-345+6789"], [-2668, "1-2-3456+789"], [-34479, "1-2-34567+89"],
[-345670, "1-2-345678+9"], [-456787, "1-2+3-456789"], [-56756,
"1-2+34-56789"], [-6445, "1-2+345-6789"], [2666, "1-2+3456-789"],
[34477, "1-2+34567-89"], [345668, "1-2+345678-9"], [56763,
"1-23-4+56789"], [6722, "1-23-45+6789"], [311, "1-23-456+789"],
[-4500, "1-23-4567+89"], [-45691, "1-23-45678+9"], [-56807,
"1-23+4-56789"], [-6766, "1-23+45-6789"], [-355, "1-23+456-789"],
[4456, "1-23+4567-89"], [45647, "1-23+45678-9"], [6551,
"1-234-5+6789"], [500, "1-234-56+789"], [-711, "1-234-567+89"],
[-5902, "1-234-5678+9"], [-7017, "1-234+5-6789"], [-966,
"1-234+56-789"], [245, "1-234+567-89"], [5436, "1-234+5678-9"],
[-1561, "1-2345-6+789"], [-2322, "1-2345-67+89"], [-3013,
"1-2345-678+9"], [-3127, "1-2345+6-789"], [-2366, "1-2345+67-89"],
[-1675, "1-2345+678-9"], [-23373, "1-23456-7+89"], [-23524,
"1-23456-78+9"], [-23537, "1-23456+7-89"], [-23386, "1-23456+78-9"],
[-234565, "1-234567-8+9"], [-234567, "1-234567+8-9"], [-456789,
"1+2-3-456789"], [-56820, "1+2-34-56789"], [-7131, "1+2-345-6789"],
[-4242, "1+2-3456-789"], [-34653, "1+2-34567-89"], [-345684,
"1+2-345678-9"], [-56769, "1+23-4-56789"], [-6810, "1+23-45-6789"],
[-1221, "1+23-456-789"], [-4632, "1+23-4567-89"], [-45663,
"1+23-45678-9"], [-6559, "1+234-5-6789"], [-610, "1+234-56-789"],
[-421, "1+234-567-89"], [-5452, "1+234-5678-9"], [1551,
"1+2345-6-789"], [2190, "1+2345-67-89"], [1659, "1+2345-678-9"],
[23361, "1+23456-7-89"], [23370, "1+23456-78-9"], [234551,
"1+234567-8-9"], [56794, "12-3-4+56789"], [6753, "12-3-45+6789"],
[342, "12-3-456+789"], [-4469, "12-3-4567+89"], [-45660,
"12-3-45678+9"], [-56776, "12-3+4-56789"], [-6735, "12-3+45-6789"],
[-324, "12-3+456-789"], [4487, "12-3+4567-89"], [45678,
"12-3+45678-9"], [6762, "12-34-5+6789"], [711, "12-34-56+789"], [-500,
"12-34-567+89"], [-5691, "12-34-5678+9"], [-6806, "12-34+5-6789"],
[-755, "12-34+56-789"], [456, "12-34+567-89"], [5647, "12-34+5678-9"],
[450, "12-345-6+789"], [-311, "12-345-67+89"], [-1002,
"12-345-678+9"], [-1116, "12-345+6-789"], [-355, "12-345+67-89"],
[336, "12-345+678-9"], [-3362, "12-3456-7+89"], [-3513,
"12-3456-78+9"], [-3526, "12-3456+7-89"], [-3375, "12-3456+78-9"],
[-34554, "12-34567-8+9"], [-34556, "12-34567+8-9"], [-56778,
"12+3-4-56789"], [-6819, "12+3-45-6789"], [-1230, "12+3-456-789"],
[-4641, "12+3-4567-89"], [-45672, "12+3-45678-9"], [-6748,
"12+34-5-6789"], [-799, "12+34-56-789"], [-610, "12+34-567-89"],
[-5641, "12+34-5678-9"], [-438, "12+345-6-789"], [201,
"12+345-67-89"], [-330, "12+345-678-9"], [3372, "12+3456-7-89"],
[3381, "12+3456-78-9"], [34562, "12+34567-8-9"], [6903,
"123-4-5+6789"], [852, "123-4-56+789"], [-359, "123-4-567+89"],
[-5550, "123-4-5678+9"], [-6665, "123-4+5-6789"], [-614,
"123-4+56-789"], [597, "123-4+567-89"], [5788, "123-4+5678-9"], [861,
"123-45-6+789"], [100, "123-45-67+89"], [-591, "123-45-678+9"], [-705,
"123-45+6-789"], [56, "123-45+67-89"], [747, "123-45+678-9"], [-251,
"123-456-7+89"], [-402, "123-456-78+9"], [-415, "123-456+7-89"],
[-264, "123-456+78-9"], [-4443, "123-4567-8+9"], [-4445,
"123-4567+8-9"], [-6667, "123+4-5-6789"], [-718, "123+4-56-789"],
[-529, "123+4-567-89"], [-5560, "123+4-5678-9"], [-627,
"123+45-6-789"], [12, "123+45-67-89"], [-519, "123+45-678-9"], [483,
"123+456-7-89"], [492, "123+456-78-9"], [4673, "123+4567-8-9"], [2012,
"1234-5-6+789"], [1251, "1234-5-67+89"], [560, "1234-5-678+9"], [446,
"1234-5+6-789"], [1207, "1234-5+67-89"], [1898, "1234-5+678-9"],
[1260, "1234-56-7+89"], [1109, "1234-56-78+9"], [1096,
"1234-56+7-89"], [1247, "1234-56+78-9"], [668, "1234-567-8+9"], [666,
"1234-567+8-9"], [444, "1234+5-6-789"], [1083, "1234+5-67-89"], [552,
"1234+5-678-9"], [1194, "1234+56-7-89"], [1203, "1234+56-78-9"],
[1784, "1234+567-8-9"], [12421, "12345-6-7+89"], [12270,
"12345-6-78+9"], [12257, "12345-6+7-89"], [12408, "12345-6+78-9"],
[12279, "12345-67-8+9"], [12277, "12345-67+8-9"], [12255,
"12345+6-7-89"], [12264, "12345+6-78-9"], [12395, "12345+67-8-9"],
[123450, "123456-7-8+9"], [123448, "123456-7+8-9"], [123446,
"123456+7-8-9"]]

Well this is very impressive as it solves the quiz but I lost him
there, I guess we have to look into the block applied to tmp.map
{|x|  t = "1" + x.split(//).zip((2..9).to_a).join.delete(" ") ; [eval(t),t]}

okay let us take just one x, e.g.
x= tmp[32]
=> "-   -  +"
## To my great despair tmp[42] is not a very good example :(

Now we split x into single characters and zip the digits 2 to 9 into them
x.split(//).zip([*2..9])
=> [["-", 2], [" ", 3], [" ", 4], [" ", 5], ["-", 6], [" ", 7], [" ",
8], ["+", 9]]
and I think I understand what happened now, the rest is basic, add a 1
in the front flatten the array and delete all spaces, and you get the
expressions needed for the quiz.

I guess that the final sort.each is quite straight forward.

HTH

BTW I want to have my ball back James, or adjust my handicap please ;).

Cheers
Robert

--
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw

```