算法1

(java) $O(nlgn)$

java 代码

import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {
    public static void main(String[]args){
        Scanner sn =new Scanner(System.in);
        int N = sn.nextInt();
        int[][] data = new int[N][2];
        for(int i=0;i<N;i++){
            data[i][0]=sn.nextInt();
            data[i][1]=sn.nextInt();
        }
        Arrays.sort(data,((o1, o2) -> o1[0]-o2[0]));
        PriorityQueue<Integer> heap = new PriorityQueue <>();
        for (int i = 0; i < N; i++) {
            if(!heap.isEmpty() && data[i][0]>heap.peek())  heap.poll();     // 合并到同一个组，移除当前最小的分组
            heap.offer(data[i][1]); // 添加新的分组
        }
        System.out.println(heap.size());
    }
}