Codility - Number-of-disc-intersections Still working on it :/

number-of-disc-intersections.rb

def solution(a)
    radii = {}
    a.count.times do |c|
        (c-a[c]..c+a[c]).to_a.each do |r|
            radii[r] = [] if !radii.key?(r)
            radii[r] << c
        end
    end
    
    combs = []
    radii.keys.each do |k|
        combs << [k].product(radii[k]-[k]) if k >= 0 and k <= (a.length-1)
    end
    res = combs.flatten(1).map { |x| x.sort}.uniq

    return res.count
end