def heapSort(alist):
    if alist == None or len(alist) == 0:
        return
    length = len(alist)
    output = []
    for i in range(length):
        tempLen = len(alist)
        for j in range(tempLen//2-1, -1, -1):
            preIndex = j
            preVal, heap = alist[preIndex], False
            while 2 * preIndex < tempLen - 1 and not heap:
                curIndex = 2 * preIndex + 1
                if curIndex < tempLen - 1:
                    if alist[curIndex] < alist[curIndex+1]:
                        curIndex += 1
                if preVal >= alist[curIndex]:
                    heap = True
                else:
                    alist[preIndex] = alist[curIndex]
                    preIndex = curIndex
            alist[preIndex] = preVal
        output.insert(0, alist.pop(0))
    return output

test = [2, 6, 5, 9, 10, 3, 7]
print(heapSort(test))