题解 | #活动安排#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
import java.util.Comparator;
import java.util.PriorityQueue;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StreamTokenizer st  = new StreamTokenizer(br);
        PriorityQueue<int[]> heap = new PriorityQueue<>(
            Comparator.comparingInt(a -> a[1])
        );
        st.nextToken();
        int n = (int)st.nval;
        for (int i = 0; i < n; i++) {
            st.nextToken();
            int a = (int)st.nval;
            st.nextToken();
            int b = (int)st.nval;
            heap.add(new int[] {a, b});
        }
        int count = 0;
        int end = 0;
        while (!heap.isEmpty()) {
            int[] pre = heap.remove();
            if (pre[0] >= end) {
                count++;
                end = pre[1];
            }
        }
        System.out.println(count);
    }
}