求k个最小元素， 华为

Posted 2020-12-16 li修远

Java 大根堆，维护k个最小的元素，时间复杂度O(KlogK)。

import java.util.*;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt(), k = sc.nextInt();
            PriorityQueue<Integer> q = new PriorityQueue<>(Collections.reverseOrder());
            for(int i=0; i < n; i++) {
                int t = sc.nextInt();
                if(q.isEmpty() || q.size() < k) q.offer(t);
                else {
                    int min = q.peek();
                    if(t < min) {
                        q.poll();
                        q.offer(t);
                    }
                }
            }
            ArrayList<Integer> res = new ArrayList<>();
            while(!q.isEmpty()) res.add(q.poll());
            for(int i=k-1; i > 0; i--) 
                System.out.print(res.get(i) + " ");
            System.out.println(res.get(0));
        }
    }
}