* sample/trick2015/: added the award-winning entries of TRICK 2015.

See https://github.com/tric/trick2015 for the contest outline.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53041 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

sample/trick2015/eregon/authors.markdown

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+* Benoit Daloze (eregon)
+  * eregontp@gmail.com
+  * cctld: be

sample/trick2015/eregon/entry.rb

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+class String;def[]*a;$*<<a;b;end;end;
+_=0;z="C=Fiber;s=$*;a=*0..8;l=C.new{e
+xit},*a.product(a).select{|r,c|s[r][c
+]==0}."[1,9,_, _,_,8, _,_,5]+"map{|r,
+c|C.ne"[_,_,2, _,5,_, _,8,9]+"w{o=s[r
+][c];l"[8,_,6, 7,4,_, _,_,_]+"oop{(1.
+.9).map{|n|C.yield(s[r][c]=n)if a.non
+e?{|k|"[_,_,_, _,_,4, _,9,2]+"s[r][k]
+==n||s"[_,2,3, _,7,_, 8,1,_]+"[k][c]=
+=n||s["[5,6,_, 8,_,_, _,_,_]+"r-r%3+k
+%3][c-c%3+k/3]==n}};s[r][c]=o;C.yield
+}}},C."[_,_,_, _,2,7, 9,_,3]+"new{loo
+p{puts"[9,3,_, _,8,_, 1,_,_]+" s.map{
+|r|r*'"[2,_,_, 5,_,_, _,4,8]+" '}<<''
+;C.yield}};c=l[i=1];loop{c=l[i+=c.res
+ume ? 1:-1]}";eval z.tr ?\n,''

sample/trick2015/eregon/remarks.markdown

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+### Remarks
+
+Just run it without arguments:
+
+    ruby entry.rb
+
+I confirmed the following implementations and platforms:
+
+* Linux:
+  * ruby 2.3.0dev (2015-10-30 trunk 52394) [x86\_64-linux]
+  * ruby 2.2.2p95 (2015-04-13 revision 50295) [x86\_64-linux]
+  * ruby 2.0.0p647 (2015-08-18) [x86\_64-linux]
+* Darwin:
+  * ruby 2.0.0p247 (2013-06-27 revision 41674) [x86\_64-darwin10.8.0]
+  * jruby 9.0.3.0 (2.2.2) 2015-10-21 633c9aa Java HotSpot(TM) 64-Bit Server VM 25.11-b03 on 1.8.0\_11-b12 +jit [darwin-x86\_64]
+  * rubinius 2.2.6.n74 (2.1.0 94b3a9b4 2014-03-15 JI) [x86\_64-darwin12.5.0]
+
+### Description
+
+This program shows all solutions of any sudoku puzzle.
+
+The embedded sudoku puzzle can be changed at wish.
+
+Giving an empty puzzle (all `0` or `_`), the program will print every possible completed sudoku puzzle.
+We do not however make any time guarantee on such behavior.
+
+The program is rather small for the task: the solver is actually 302 characters long,  
+assuming the sudoku puzzle is in a variable `s` and encoded as an array of rows of numbers.
+
+### Internals
+
+* The program implements backtracking and keeps state in a very elegant way.
+* The whole program never goes deeper than 9 stack frames,
+  but yet can backtrack up to 81 levels!
+* The main loop of a program is a dance between cells.
+  On one end is the solutions, on the other the program ends.
+* The program only uses *infinite* loops and no `break`.
+* The program interleaves the creation of the solver and the puzzle.
+* The program is easy to deobfuscate but finding how it works will be more challenging.
+* The last line contains a smiley.
+
+The author likes good numbers:
+
+    $ wc entry.rb
+          15      42     600
+
+The inspiration for this entry comes from:
+
+* A newspaper sudoku with multiple solutions
+* An inspiring paper: `Revisiting Coroutines`
+
+Various tricks used for brevity:
+
+* The method defined is one of the fews which may contain neither parenthesis nor spaces.
+* The program uses the return value of Fiber.yield without arguments.
+* `String#b` is used as a very short `self`.
+
+Design issues:
+
+* Since `return`-ing from a Fiber is not allowed, the programs must `exit`.
+* The program reveals that the cartesian product operator is still too long: `a.product(a)` while it could be `a*a`.
+
+Note:
+
+* In the original code, the last cell was: `C.new{loop{yield s; C.yield}}`,
+  implementing some sort of "forwarding coroutine".
+
+### Limitation
+
+* The program does not want any *argument* with you and will quit quietly if you try some.