heap sort test code

heap.py

# implemented according to the psudocode from:
# http://en.wikipedia.org/wiki/Heapsort (2013/03/05)

def heapSort(unsortedList):
    heapify(unsortedList)
    end = len(unsortedList) - 1
    while end > 0:
        unsortedList[end], unsortedList[0] = unsortedList[0], unsortedList[end]
        end -= 1
        shiftDown(unsortedList, 0, end)

def heapify(unsortedList):
    start = (len(unsortedList) - 2) / 2
    while (start >= 0):
        shiftDown(unsortedList, start, len(unsortedList) - 1)
        start -= 1

def shiftDown(unsortedList, start, end):
    root = start
    while root * 2 + 1 <= end:
        child = root * 2 + 1
        swap = root
        if unsortedList[root] < unsortedList[child]:
            swap = child
        child += 1
        if child <= end and unsortedList[swap] < unsortedList[child]:
            swap = child
        if swap != root:
            unsortedList[swap], unsortedList[root] = unsortedList[root], unsortedList[swap]
            root = swap
        else:
            return

if __name__ == '__main__':
    a = [0, 1, 999, 1, 1]
    heapSort(a)
    print a