Heap Sort 实现(MIT Algorithm Course)

根据算法导论实现。有个小缺陷，heapsort中result是逆序排序。

def parent(i):
	return i%2;

def left(i):
	return 2*i+1;

def right(i):
	return 2*(i+1);

def maxHeapify(numList,i):
    l = left(i);
    r = right(i);
    if l<= len(numList)-1 and numList[l] > numList[i]:
        largest = l;
    else:
        largest = i;
    if r<= len(numList)-1 and numList[r] > numList[largest]:
        largest = r;
    if largest != i:
        numList[i], numList[largest] = numList[largest], numList[i]; #swap
        maxHeapify(numList,largest);

def buildMaxHeap(numList):
    heapsize = len(numList);
    for i in range(len(numList)//2-1,-1,-1):
        maxHeapify(numList,i);

def heapSort(numList):
    global alist;
    alist = numList;
    result= [];
    buildMaxHeap(alist);
    for i in range(len(alist)-1,0,-1):
        alist[0], alist[i] = alist[i], alist[0];
        #print(alist[i]);
        #print(i);
        result.append(alist.pop(i));
        maxHeapify(alist,0);
    result.append(alist.pop());
    return result;

从Stackoverflow找到的一种实现方式

def swap(i, j):                    
    sqc[i], sqc[j] = sqc[j], sqc[i] 

def heapify(end,i):   
    l=2 * i + 1  
    r=2 * (i + 1)   
    max=i   
    if l < end and sqc[i] < sqc[l]:   
        max = l   
    if r < end and sqc[max] < sqc[r]:   
        max = r   
    if max != i:   
        swap(i, max)   
        heapify(end, max)   

def heap_sort():     
    end = len(sqc)   
    start = end // 2 - 1 # use // instead of /
    for i in range(start, -1, -1):   
        heapify(end, i)   
    for i in range(end-1, 0, -1):   
        swap(i, 0)   
        heapify(i, 0)   

sqc = [2, 7, 1, -2, 56, 5, 3]
heap_sort()
print(sqc)