Question

I have an array like [1,1,1,2,4,6,3,3] and I would like to get the list of repeated elements, in this case [1,3]. I wrote this:

my_array.select{|obj|my_array.count(obj)>1}.uniq 

But it is tragically inefficient (o(n²)). Do you have a better idea? If possible concise.

Thanks

Answer 1

Inspired by Ilya Haykinson’s answer:

def repeated(array)   counts = Hash.new(0)   array.each{|val|counts[val]+=1}   counts.reject{|val,count|count==1}.keys end