/**
* File: top_k.cs
* Created Time: 2023-06-14
* Author: hpstory (hpstory1024@163.com)
*/

namespace hello_algo.chapter_heap; 

public class top_k {
    /* 基于堆查找数组中最大的 k 个元素 */
    public static PriorityQueue<int, int> topKHeap(int[] nums, int k) {
        PriorityQueue<int, int> heap = new PriorityQueue<int, int>();
        // 将数组的前 k 个元素入堆
        for (int i = 0; i < k; i++) {
            heap.Enqueue(nums[i], nums[i]);
        }
        // 从第 k+1 个元素开始，保持堆的长度为 k
        for (int i = k; i < nums.Length; i++) {
            // 若当前元素大于堆顶元素，则将堆顶元素出堆、当前元素入堆
            if (nums[i] > heap.Peek()) {
                heap.Dequeue();
                heap.Enqueue(nums[i], nums[i]);
            }
        }
        return heap;
    }

    [Test]
    public void Test() {
        int[] nums = { 1, 7, 6, 3, 2 };
        int k = 3;
        PriorityQueue<int, int> res = topKHeap(nums, k);
        Console.WriteLine("最大的 " + k + " 个元素为");
        PrintUtil.PrintHeap(res);
    }
}
