Counting sort a list in descending order

Question

So basically I want to figure out how to reverse a counting sort. This is the code I found:

def countingSort(myList):
    maxValue = 0
    for i in range(len(myList)):
        if myList[i] > maxValue:
            maxValue = myList[i]

    buckets = [0] * (maxValue + 1)

    for i in myList:
        buckets[i] += 1

    i = 0
    for j in range(maxValue + 1):
         for a in range(buckets[j]):
             myList[i] = j
             i += 1

    return myList

if __name__ == '__main__':
    sortedList = countingSort([1,23,4,5,6,7,8])
    print(sortedList)

So I decided to change line 16 to this:

i -= 1

The results are very close, but I get this:

[1, 23, 8, 7, 6, 5, 4]

My issue is that 1 is before 23 for some reason. I tried reverting some of the other signs, but it usually results in an out of bounds error. Any ways to work around it?

Answer 1

Reverse the range that j iterates through so you start from high numbers then end with low numbers:

for j in range(maxValue, -1, -1):

Answer 2

With i -= 1 you're writing at indices 0, -1, -2, -3 etc. That is, you write the smallest number (the 1) at the front, and then the remaining numbers from the back backwards. You can make it work by starting with i = -1 .