TopK

网易面试挂了，伤心。

一面面试官不是搞技术的，二面面试官搞ios，全程不问JVM，并发的知识，运气真差

而且手撸代码硬伤，没得编译

准备先在IDE敲一遍，在再纸上面写一遍。

package com.qiuzhao.test;

import java.util.PriorityQueue;
import java.util.Queue;

/**
 * @Auther: Chang
 * @Date: 2018/8/27
 */
public class topK {
    public static void main(String[] args) {

        int[] a = {489, 500, 111, 100, 2, 7, 3, 8, 66, 888};
        int k = 3;
        // 第一种 推排序
        prioritySort(a, k);
        // 第二种 快速排序
        quickSort(a, k);
    }

    // 堆排序 int[] a = {489, -5, 111, 100, 2, 7, 3, 8, 66, 88};
    private static void prioritySort(int[] a, int k) {
        Queue<Integer> pq = new PriorityQueue<>(k);
        for (int i = 0; i < a.length; i++) {
            int n = pq.size();
            if (n >= k && a[i] > pq.peek()) {
                pq.poll();
            }
            n = pq.size();
            if (n < k) pq.add(a[i]);
        }
        pq.forEach(x -> System.out.print(x + "  "));
        System.out.println();
    }

    private static void quickSort(int[] a, int k) {

        int left = 0;
        int right = a.length - 1;
        int mid = partition(a, left, right);
        while (mid != k) {
            if (mid > k) {
                right = mid - 1;
                mid = partition(a, left, right);
            } else {
                left = mid + 1;
                mid = partition(a, left, right);
            }
        }
        for (int i = 0; i < mid; i++) {
            System.out.print(a[i] + "  ");
        }
        System.out.println();
    }

    private static int partition(int[] a, int left, int right) {

        int temp = a[left];
        while (left < right) {
            while (left < right && a[right] <= temp) right--;
            a[left] = a[right];
            while (left < right && a[left] >= temp) left++;
            a[right] = a[left];
        }
        a[left] = temp;
        return left;
    }
}