Algrithom

fibonaci.rb

def fibonaci1(n)
  return n if n <= 1
  fibonaci1(n - 1) + fibonaci1(n - 2)
end

def fibonaci2(n)
  helper = lambda do |a, b, i|
    return b if i <= 1
    helper.call(b, a + b, i - 1)
  end
  helper.call(0, 1, n)
end

p fibonaci1(10)
p fibonaci2(10)

quick_sort.rb

def quick_sort(arr)
  quick_sort_helper(arr, 0, arr.count - 1)
end

def quick_sort_helper(arr, p, r)
  if p < r
    q, arr = partition(arr, p, r)
    quick_sort_helper(arr, p, q - 1) + quick_sort_helper(arr, q + 1, r)
  end
  arr
end

def partition(arr, p, r)
  x = arr[r]
  i = p - 1
  (p..r-1).each do |j|
    n = arr[j]
    if n <= x
      i += 1
      arr[i], arr[j] = n, arr[i]
    end
  end
  arr[i + 1], arr[r] = arr[r], arr[i + 1]
  [i + 1, arr]
end

arr = [2, 8, 7, 1, 3, 5, 6, 4]
p quick_sort(arr)

# ruby style
def quick_sort2(arr)
  return [] if arr == []
  x, *xs = *arr
  left, right = xs.partition { |n| n < x }
  quick_sort2(left) + [x] + quick_sort2(right)
end

p quick_sort2(arr)