我正在做一项作业,用 Ruby 编写递归归并排序算法。我试图将其逐个分解,以便能够围绕它进行思考。到目前为止,我所做的是尝试完成“划分”步骤,直到每个数组中只剩下一个元素。
a = [5, 2, 4, 6, 1, 7, 3, 8]
def divide(arr)
return arr if arr.length < 2
else
arr1 = puts divide(arr[0..arr.length/2-1])
arr2 = puts divide(arr[arr.length/2..arr.length])
end
我认为输出将是:
[5] [8]
但是它打印出来:
5
2
4
6
1
7
3
8
它是如何工作的?
最佳答案
你至少有两个问题。
首先,else
声明没有效果,这不是你怎么做if else
在 Ruby 中。
其次,如果a.length < 2
是false
那么你的方法将返回 nil
. puts
返回 nil
, x = nil
返回 nil
.
我添加了一些打印件来演示您的代码如何工作,希望对您有所帮助:
$level = 0
def divide(arr)
return arr if arr.length < 2
$level += 1
puts "Working with array #{arr}"
arr1 = divide(arr[0..arr.length/2-1])
puts "Level = #{$level} arr1 = #{arr1}"
arr2 = divide(arr[arr.length/2..arr.length])
puts "Level = #{$level} arr2 = #{arr2}"
$level -= 1
nil
end
divide([5, 2, 4, 6, 1, 7, 3, 8])
输出:
Working with array [5, 2, 4, 6, 1, 7, 3, 8]
Working with array [5, 2, 4, 6]
Working with array [5, 2]
Level = 3 arr1 = [5]
Level = 3 arr2 = [2]
Level = 3 arr1 =
Working with array [4, 6]
Level = 4 arr1 = [4]
Level = 4 arr2 = [6]
Level = 4 arr2 =
Level = 4 arr1 =
Working with array [1, 7, 3, 8]
Working with array [1, 7]
Level = 6 arr1 = [1]
Level = 6 arr2 = [7]
Level = 6 arr1 =
Working with array [3, 8]
Level = 7 arr1 = [3]
Level = 7 arr2 = [8]
Level = 7 arr2 =
Level = 7 arr2 =
关于arrays - Ruby 合并排序——这个递归函数是如何工作的?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45909315/