就地快速排序-python

Question

I'm trying to implement quicksort in python in-place. I followed the pseudocode from the wikipedia article here, but this is not producing a sorted list. Does anything seem glaringly incorrect?

# Perform QuickSort in place
def partition(arr,low,high):
    pivotIndex = random.randint(0,high)
    pivotValue = arr[pivotIndex]

    currentIndex = low

    t = arr[high]
    arr[high] = pivotValue
    arr[pivotIndex] = t

    for i in range(low,high-1):
        if arr[i] < pivotValue:
            t = arr[i]
            arr[i] = arr[currentIndex]
            arr[currentIndex] = t
            currentIndex += 1
    t = arr[currentIndex]
    arr[currentIndex] = arr[high]
    arr[high] = t
    return currentIndex

def quickSort(arr,low,high):
    # pick partition
    if low < high:
        part = partition(arr,low,high)
        quickSort(arr,low,part-1)
        quickSort(arr,part+1,high)

arr = [1,3,6,7,9,10]
quickSort(arr,0,len(arr)-1)
print arr

Answer 1

Well, the first line of the partition function is clearly wrong:

pivotIndex = random.randint(0, high)

This should obviously be low instead of 0 .

Your range values might be off... I don't think you need to subtract 1 from high .

Answer 2

Also, in Python you don't have to use a temporal variable to do an exchange.

Instead of:

t = x
x = y
y = t

You can do:

x, y = y, x

Answer 3

Did you remember to import random ? Also, in order to see the difference, your array must be an unsorted one. If the elements are already in the correct order, how can you find the difference?

Also, by listing all the arrays as arr , it can get confusing. I noticed that all functions with arr in them are using arr as the corresponding parameter. Why not do something do distinguish them?