my codility solutions

eighth.rb

def solution(a)
   counter = [0] * a.length
  a.each do |element|
    if ! (1 <= element && element <= a.length)
      return 0
    else
      if counter[element-1] != 0
        return 0
      else
        counter[element-1] = 1
      end
    end

  end
  1
end

fifth.rb

def solution(a)
  sumright = a[1..-1].reduce(:+)
  sumleft = a[0]
  min = (sumright - sumleft).abs
  a[1..-2].each do |element|
    sumleft += element
    sumright -= element

    if ((sumright - sumleft).abs < min)
      min = (sumright - sumleft).abs
    end
  end
  min
end

first.rb

def solution(n)
  max_gap = 0
  current_gap = 0
  a = n.to_s(2).split('').each do |number|
    if number == "1"
      if current_gap > max_gap
        max_gap = current_gap
      end
      current_gap = 0
    elsif number == "0"
      current_gap += 1
    end
  end
  max_gap
end

fourth.rb

def solution(x, y, d)
  (y - x) % d == 0 ? (y - x) / d :
    ((y - x) / d) + 1
end

second.rb

def solution(a, k)
  if k == 0
    return a
  else
    result = []
    a.each_with_index do |value, index|
      result.push(a[index - 1])
    end
    solution(result, k - 1)
  end
end

seventh.rb

def solution(x, a)
    cache = []
  i = 0
  a.each do |element|
    if !cache[element]
      cache[element] = true
      x -= 1
    end
    if (x == 0)
      return i
    end
    i += 1
  end
  -1

end

sixth.rb

def solution(a)
  n = a.length + 1
  total = (n * (n + 1)) / 2
  total - (a.inject(:+) || 0)
end

third.rb

def solution(a)
  a.inject(0) {|sum, element| sum = sum ^ element }
end