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

 #!/usr/bin/env python3

 def heap_sort(ary, num):
         def siftdown(ary, e, begin, end):
                 i,j = begin, begin*2+1
                 while j < end:
                         if j+1 < end and ary[j+1] < ary[j]:
                                 j += 1
                         if e < ary[j]:
                                 break
                         ary[i] = ary[j]
                         i,j = j,j*2+1
                 ary[i] = e

         end = len(ary)
         for i in range(end//2-1, -1, -1):
                 siftdown(ary, ary[i], i, end)

         #方法1
         for i in range(end-1, -1, -1):
                 e = ary[i]
                 ary[i] = ary[0]
                 siftdown(ary, e, 0, i)
         return ary[:-num-1:-1]

         #方法2
         """
         li = []
         for i in range(num):
                 if len(ary) > i:
                         li.append(ary[0])
                         e = ary[end-1-i]
                         siftdown(ary, e, 0, end-1-i)
                 else:
                         break
         return li
         """

 if __name__ == '__main__':
         a = [4,5,1,6,2,7,3,8]
         num = int(input("最小的k个数:"))
         print(heap_sort(a,num))