円周上のCrossing

どういうわけか入力がC/C++/Java用なので、採点プログラムを
https://github.com/cielavenir/procon/commit/38b0ad5bedaefc507fb32b5b5866046a51ddad50
に用意しました…。

hena14pre.rb

#!/usr/bin/env ruby
#http://qiita.com/Nabetani/items/66806c9dc14a96f2fd42
#http://nabetani.sakura.ne.jp/hena/ord14crosscircle/
STDOUT.sync=true
while gets
    l=$_.chomp.split('')
    a=l.uniq.map{|e|
        l.each_with_index.select{|f|e==f[0]}.map{|f|f[1]}
    }
    # aabbca1bcb -> [[0, 1, 5], [2, 3, 7, 9], [4, 8], [6]]
    n=0
    a.size.times{|i|
        # a[i]角形の対角線の交点の個数はa[i]C4
        n+=(a[i].size-3..a[i].size).reduce(:*)/24 if a[i].size>3
        (i+1).step(a.size-1){|j|
            a[i].combination(2){|c,d|
                a[j].combination(2){|e,f|
                    e_inside=c<e&&e<d
                    f_inside=c<f&&f<d
                    n+=1 if e_inside^f_inside
                }
            }
        }
    }
    puts n
end