算法回鍋肉——計數排序

示例代碼純粹是爲了加深印象，選擇的目標語言有更便捷的實現方式，另外去掉了一些假設條件檢查。

#encoding:gbk

Size = 20
arr = Array.new(Size) do	#初始化待排序數組，隨機填寫元素
	rand(Size)
end

def counting_sort(a,b,k)
	c = Array.new(k + 1,0) #下標數組
	a.each do |x|
		c[x] += 1	#計數
	end
	c.each_with_index do |x,i|
		next if i == 0
		c[i] += c[i - 1] #累計計數
	end
	a.each do |x|
		b[c[x] - 1] = x #放置元素
		c[x] -= 1 #爲相同輸入挪動下標
	end
end

puts arr.inspect
a = arr.clone	#輸入數組
b = Array.new(a.size,-1)	#輸出數組，初始化爲-1以便觀測
k = a.size	#下標最大值
counting_sort(a,b,k)
puts b.inspect

輸出如下：

---------- Ruby ----------
[14, 7, 18, 8, 0, 8, 14, 5, 12, 15, 6, 2, 11, 8, 12, 11, 12, 15, 9, 0]
[0, 0, 2, 5, 6, 7, 8, 8, 8, 9, 11, 11, 12, 12, 12, 14, 14, 15, 15, 18]

Output completed (1 sec consumed) - Normal Termination