编程题目： 找出最小的k个数

找出最小或者最大的几个数我使用的是堆排序，效率为0（nlgn）


构建小顶堆返回末尾的k个数 或者 构建大顶堆返回前k个数

 

 1 #!/usr/bin/env python3
 2 
 3 def heap_sort(ary, num):
 4         def siftdown(ary, e, begin, end):
 5                 i,j = begin, begin*2+1
 6                 while j < end:
 7                         if j+1 < end and ary[j+1] < ary[j]:
 8                                 j += 1
 9                         if e < ary[j]:
10                                 break
11                         ary[i] = ary[j]
12                         i,j = j,j*2+1
13                 ary[i] = e
14 
15         end = len(ary)
16         for i in range(end//2-1, -1, -1):
17                 siftdown(ary, ary[i], i, end)
18 
19         #方法1
20         for i in range(end-1, -1, -1):
21                 e = ary[i]
22                 ary[i] = ary[0]
23                 siftdown(ary, e, 0, i)
24         return ary[:-num-1:-1]
25 
26         #方法2
27         """
28         li = []
29         for i in range(num):
30                 if len(ary) > i:
31                         li.append(ary[0])
32                         e = ary[end-1-i]
33                         siftdown(ary, e, 0, end-1-i)
34                 else:
35                         break
36         return li       
37         """
38 
39 if __name__ == '__main__':
40         a = [4,5,1,6,2,7,3,8]
41         num = int(input("最小的k个数:"))
42         print(heap_sort(a,num))

 

posted @ 2017-02-23 18:22  小黄人python  阅读(1392)  评论(0)  编辑  收藏  举报