Binary Search.

binary_search.rb

def iterative_binary_search(array, value)
  start = 0
  top = array.size - 1

  while top >= start
    middle = (start + top) / 2
    if array[middle] == value
      return middle
    elsif array[middle] > value
      top = middle - 1
    else
      start = middle + 1
    end
  end

  raise StandardError, 'Cannot search. Maybe an array is not sorted or value out of the range of the array?'
end

def recursive_binary_search(array, value, start = 0, top = nil)
  top ||= array.length - 1
  middle = (start + top) / 2

  if start > top
    raise StandardError, 'Cannot search. Maybe an array is not sorted or value out of the range of the array?'
  end

  if array[middle] == value
    middle
  elsif array[middle] > value
    top = middle - 1
    recursive_binary_search(array, value, start, top)
  else
    start = middle + 1
    recursive_binary_search(array, value, start, top)
  end
end