split_array_codility.md

def solution(x, arr)
  
  k = 0
  n = arr.length
  
  condition = -> (a) { a.eql? x}
  
  arr.each_with_index do |a, i|
    if arr[0..i-1].select(&condition).size == arr[i..n-1].reject(&condition).size
      k = i
      break
    end
  end
  k
end

#usage
arr = [5, 5, 1, 7, 2, 3, 5]
x = 5

k = solution(x, arr)
#=> 4