09_heap_topK_topK问题

# 比较排序 - 通过比较来决定两个值是否交换
import random


def sift(li, low, high):

    i = low
    j = 2 * i + 1
    temp = li[low]

    while j <= high:
        if j + 1 <= high and li[j + 1] < li[j]:
            j = j + 1

        if li[j] < temp:
            li[i] = li[j]
            i = j
            j = 2 * i + 1
        else:
            break
    li[i] = temp


def topk(li, k):

    # 提取前 k 个元素建堆
    heap = li[0:k]
    for i in range((k - 2) // 2, -1, -1):
        sift(heap, i, k - 1)

    # 遍历剩下的元素，如果比堆顶大，就加进去，并对堆进行一次调整
    for i in range(k, len(li) - 1):
        if li[i] > heap[0]:
            heap[0] = li[i]
            sift(heap, 0, k - 1)

    # 挨个出数
    for i in range(k - 1, -1, -1):
        heap[0], heap[i] = heap[i], heap[0]
        sift(heap, 0, i - 1)

    return heap