Find Fixed Point in Sorted Array Algorithm

find_fixed_point.rb

def find_fixed_point(array)
    n = array.length
    high = n - 1
    low = 0

    while low <= high
      mid = low + (high - low / 2)

      if array[mid] == mid
        return mid
      elsif array[mid] < mid
        low = mid + 1
      else
        high = mid - 1
      end
    end

    # if no fixed point exist
    return -1
  end