List index out of range

Question

I was implementing quicksort in python

#QuickSort python

def sort(array):

    leftside = []
    rightside = []
    equal = []

    pivot = array[0]

    if (len(array)>1):
        for item in array:
            if item < pivot:
                leftside.append(item)
            if item > pivot:
                rightside.append(item)
            if item == pivot:
                equal.append(item)
    else:
        print array


    print sort(leftside) + equal + sort(rightside)

array = [1,2,5,4,6,2,3]
sort(array)

I get the error "pivot = array[0] IndexError: list index out of range", I don't see anything that could cause out of index error in this code. Could you please take a look?

It's the recursive call that eventually passes an empty list to sort and, naturally, `pivot = array[0]` chokes on it... — zwer, May 20 '17 at 00:08
this is duplicate with: http://stackoverflow.com/questions/18262306/quicksort-with-python — jose_bacoy, May 20 '17 at 00:18

stanleyli · Accepted Answer · 2017-05-20T00:16:48.080

0

pivot = array[0] should be in if (len(array)>1):. Otherwise you may try to do it on an empty array.

Made some other quick fixes. See how this works:

#QuickSort python

def sort(array):

    leftside = []
    rightside = []
    equal = []

    if (len(array)>1):
        pivot = array[0]
        for item in array:
            if item < pivot:
                leftside.append(item)
            if item > pivot:
                rightside.append(item)
            if item == pivot:
                equal.append(item)
        return sort(leftside) + equal + sort(rightside)
    else:
        return array


array = [1,2,5,4,6,2,3]
print(sort(array))

edited May 20 '17 at 00:16

answered May 20 '17 at 00:08

stanleyli

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Ah, Thanks for the answer. But, when I do that, I get "RuntimeError: maximum recursion depth exceeded". – tori May 20 '17 at 00:10
@tori Yes, I realized that -- tried to fix some other issues for you. Please refer to something like http://interactivepython.org/courselib/static/pythonds/SortSearch/TheQuickSort.html to see how others write quicksort in Python – stanleyli May 20 '17 at 00:14

List index out of range

1 Answers1