Question

我已经实现了计算数组反转的算法（它也合并了数组），但是为了使它更加整洁，我想对输出进行排序和计数。

Method * count_and_sort *返回数组[number_of_inversions，[sorted_array]]。方法 inversions 和* merge_sort *应该分别返回number_of_inversions和[sorted_array]，但我得到 NoMethodError

我错过了什么？

class Array

    def inversions
        count_and_sort[0]
    end

    def merge_sort
        count_and_sort[1]
    end

    def merge_sort!
        replace merge_sort
    end

private

    def count_and_sort
        return [0, self] if self.size <= 1
        left, right = partition.with_index{ |value, index| index < self.size / 2}
        left = left.count_and_sort
        right = right.count_and_sort
        merged = merge(left[1], right[1])

        [left[0] + right[0] + merged[0], merged[1]]
    end

    def merge(left, right)
        inversions = 0
        merged = []
        until left.empty? || right.empty?
            if left.first < right.first
                merged << left.shift
            else
                merged << right.shift
                inversions += left.size
            end
        end

        merged += left += right
        [inversions, merged]
    end
end

p [*1..20].shuffle.inversions

我尝试用

替换 inversions

def inversions
    result = self.send(:count_and_sort)
    result[0]
end

但结果是一样的。

PS欢迎任何其他批评和评论;）

Answer 1

错误在count_and_sort方法内，如错误消息所示：

... in 'count_and_sort': private method 'count_and_sort' called for ...

错误的行是：

left = left.count_and_sort
right = right.count_and_sort

Ruby中的私有方法无法使用显式接收器调用，必须在self上隐式调用它们。因此，您可以使count_and_sort方法受到保护，也可以使用send和left上的right进行调用。在这种情况下，我会建议前者。

调用私有方法问题

1 个答案: