|
@@ -1,49 +0,0 @@
|
|
-"""
|
|
|
|
-在海量数据中选取topK个数据:
|
|
|
|
-整个操作中,遍历数组需要O(n)的时间复杂度,每次调整小顶堆的时间复杂度是O(logK),加起来就是O(nlogK)的复杂度;
|
|
|
|
-如果K远小于n的话,O(nlogK)其实就接近于O(n),甚至会更快,因此也是十分高效的.
|
|
|
|
-"""
|
|
|
|
-
|
|
|
|
-# 构建大顶堆
|
|
|
|
-def heapify(arr, n, i, dim):
|
|
|
|
- largest = i
|
|
|
|
- left = 2*i + 1
|
|
|
|
- right = 2*i + 2
|
|
|
|
- # 与左节点进行比较
|
|
|
|
- if left < n and arr[i][dim] < arr[left][dim]:
|
|
|
|
- largest = left
|
|
|
|
- # 与左节点比较后再与右节点进行比较
|
|
|
|
- if right < n and arr[largest][dim] < arr[right][dim]:
|
|
|
|
- largest = right
|
|
|
|
- # 通过上面跟左右节点比较后,得出三个元素之间较大的下标
|
|
|
|
- # 若较大下标不是父节点的下标,说明交换后需要重新调整大顶堆
|
|
|
|
- if largest != i:
|
|
|
|
- arr[i], arr[largest] = arr[largest], arr[i]
|
|
|
|
- # 重新调整大顶堆
|
|
|
|
- heapify(arr, n, largest, dim)
|
|
|
|
-
|
|
|
|
-# 堆排序
|
|
|
|
-def heap_sort(arr, topk=None, dim=1):
|
|
|
|
- n = len(arr)
|
|
|
|
- # 构造大顶堆,从非叶子节点开始倒序遍历,因此是l//2 -1 就是最后一个非叶子节点
|
|
|
|
- for i in range(n//2-1, -1, -1):
|
|
|
|
- heapify(arr, n, i, dim)
|
|
|
|
- # 若topk不为None,则进行设定
|
|
|
|
- topk = n if topk > n or topk is None else topk
|
|
|
|
- res_list = []
|
|
|
|
- # 上面的循环完成了大顶堆的构造,那么就开始把根节点跟末尾节点交换,然后重新调整大顶堆
|
|
|
|
- for i in range(n-1, n-1-topk, -1):
|
|
|
|
- res_list.append(arr[0])
|
|
|
|
- arr[0] = arr[i]
|
|
|
|
- # arr[i], arr[0] = arr[0], arr[i]
|
|
|
|
- heapify(arr, i, 0, dim)
|
|
|
|
-
|
|
|
|
- return res_list
|
|
|
|
- # return arr[n-topk:][::-1]
|
|
|
|
-
|
|
|
|
-if __name__ == "__main__":
|
|
|
|
- arr = [[0,12], [1,11], [2,13], [3,5], [4,6], [5,7]]
|
|
|
|
- arr = heap_sort(arr, 3)
|
|
|
|
- print ("排序后")
|
|
|
|
- for i in range(len(arr)):
|
|
|
|
- print(arr[i])
|
|
|