quicksort.rb

#!/usr/bin/ruby
def partition(ar, start, stop) 
    pivot = ar[stop]
    pindex = start
        
    for i in (start..stop-1) do
        if ar[i] <= pivot
            ar[i], ar[pindex] = ar[pindex], ar[i]
            pindex += 1
        end
    end
    ar[pindex], ar[stop] = ar[stop], ar[pindex]
    return pindex
end

def quicksort(ar, start, stop)
    if start < stop
        p = partition(ar, start, stop)
        quicksort(ar, start, p-1)
        quicksort(ar, p+1, stop)
    end
    return ar
end

ar = STDIN.gets.chomp.split(" ").map{|x|x.to_i};
puts quicksort(ar, 0, ar.length - 1)