堆排序Python实现 [英] Heap sort Python implementation

问题描述

def heap_sort(nos):
    global size
    size = len(nos)
    print "the size of the List is : %d " %size
    Build_heap(size,nos)
    for i in range(size-1,0,-1):
        nums[0],nums[i] = nums[i],nums[0]
        size = size-1
        print "\n", nums
        heapify(nos,i,size)
    print "heap sort array:" ,nums

def left_child(i):
    return 2*i+1

def right_child(i):
    return 2*i+2

def heapify(nums,i,size):
    l = left_child(i)
    r = right_child(i)
    if l <= size and r <= size:
        if r != size:
            if nums[l] >= nums[r]:
                max = nums[l]
                max_index = l
            elif nums[l] <= nums[r]:
                max = nums[r]
                max_index = r
            if nums[i] >= max:
                print nums
                return
            elif nums[i] <= max:
                nums[i],nums[max_index] = max,nums[i]
                heapify(nums,max_index,size)
        else:
            nums[i],nums[l] = nums[l],nums[i]
            print nums

# build a heap A from an unsorted array          
def Build_heap(size,elements):
    iterate = size//2-1
    for i in range(iterate,-1,-1):
        print "In %d iteration" %i
        heapify(elements,i,size)
    print "heapified array is : " ,elements


if __name__ == '__main__':
    #get input from user
    nums = [6,9,3,2,4,1,7,5,10]
    #sort the list
    heap_sort(nums)

我得到的输出是这样的：

Output which I get is something like this:

the size of the List is : 9 
In 3 iteration
[6, 9, 3, 10, 4, 1, 7, 5, 2]
In 2 iteration
[6, 9, 7, 10, 4, 1, 3, 5, 2]
In 1 iteration
[6, 10, 7, 9, 4, 1, 3, 5, 2]
[6, 10, 7, 9, 4, 1, 3, 5, 2]
In 0 iteration
[10, 6, 7, 9, 4, 1, 3, 5, 2]
[10, 9, 7, 6, 4, 1, 3, 5, 2]
[10, 9, 7, 6, 4, 1, 3, 5, 2]
heapified array is :  [10, 9, 7, 6, 4, 1, 3, 5, 2]
heap sort array: 
[9, 7, 6, 4, 1, 3, 5, 2, 10]

我尝试在python中实现堆排序算法。最终输出未排序。我试图找出在heapify操作中出了点问题，但我找不到。

I tried implementing a heap sort algorithm in python. The final output is not sorted. There is something wrong in the heapify operation which I tried to figure out, but I couldn't find it.

有人可以指出我的代码有什么问题并提出一个建议吗？

Can someone point out what's wrong in my code and propose a solution for it?

推荐答案

第一个项目（ 0 ）已交换？与最后一项。要保持最大堆空间不变，应使用 0 调用heapify。

The first item(0) was swaped with the last item. To keep max-heap invairant, you should call heapify with 0.

def heap_sort(nos):
    size = len(nos)
    build_heap(size,nos)
    for i in range(size-1,0,-1):
        nums[0],nums[i] = nums[i],nums[0]
        size -= 1
        heapify(nos, 0, size) # <--- i -> 0

这篇关于堆排序Python实现的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！