Question

我这里有一个快速排序程序，但结果似乎有问题。我认为在引用某些值时，下面突出显示的区域肯定存在一些问题。有什么建议吗？

#where l represents low, h represents high
def quick(arr,l,h):
    #is this the correct array for quicksorting?
    if len(x[l:h]) > 1:
        #r is pivot POSITION
        r = h
        #R is pivot ELEMENT
        R = arr[r]
        i = l-1
        for a in range(l,r+1):  
            if arr[a] <= arr[r]:
                i+=1
                arr[i], arr[a] = arr[a], arr[i]
        #should I take these values? Note that I have repeated elements below, which is what I want to deal with
        quick(arr,l,arr.index(R)-1)
        quick(arr,arr.index(R)+arr.count(R),h)

x = [6,4,2,1,7,8,5,3]

quick(x,0,len(x)-1)

print(x)

Answer 1

        #should I take these values? Note that I have repeated elements below, which is what I want to deal with
        quick(arr,l,arr.index(R)-1)
        quick(arr,arr.index(R)+arr.count(R),h)

您似乎假设等于pivot元素的值已经连续。对于当前的实现，这种假设可能是错误的。测试它，例如通过在递归之前输出完整列表。

为了使假设成立，分为三组而不是两组，如at Wikipedia所述。

Answer 2

请检查一下。我想你找到答案了。

def partition(array, begin, end):
    pivot = begin
    for i in xrange(begin+1, end+1):
        if array[i] <= array[begin]:
            pivot += 1
            array[i], array[pivot] = array[pivot], array[i]
    array[pivot], array[begin] = array[begin], array[pivot]
    return pivot


def quicksort(array, begin=0, end=None):
    if end is None:
        end = len(array) - 1
    if begin >= end:
        return
    pivot = partition(array, begin, end)
    quicksort(array, begin, pivot-1)
    quicksort(array, pivot+1, end)

array = [6,4,2,1,7,8,5,3]
quicksort(array)
print (array)

Python- Quicksort程序就地

2 个答案: