9-3. 결혼식 질문있습니다.

import java.util.*;
import java.io.*;

class Main {
    static int N;
    static class Time implements Comparable<Time>{
        int time;
        char state;
        Time (int time, char state) {
            this.time = time;
            this.state = state;
        }
        public int compareTo(Time t) {
            if(time > t.time) {
                return 1;
            }else if(time == t.time) {
                if(state != t.state && t.state == 'e') {
                    return 1;
                }
            }
            return -1;
        }
    }
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;
        N = Integer.parseInt(br.readLine());

        ArrayList<Time> guests = new ArrayList<>();
        for(int i = 0; i < N; i++) {
            st = new StringTokenizer(br.readLine());
            int start = Integer.parseInt(st.nextToken());
            int end = Integer.parseInt(st.nextToken());
            guests.add(new Time(start, 's'));
            guests.add(new Time(end, 'e'));
        }
        Collections.sort(guests);

        System.out.println(solution(guests));
    }

    public static int solution(ArrayList<Time> guests) {
        int ans = 0;
        int cnt = 0;
        for(Time t : guests) {
            if(t.state == 's') {
                cnt++;
                ans = Math.max(ans, cnt);
            } else {
                cnt--;
            }
        }
        return ans;
    }
}

제가 작성한 코드는 위와 같습니다. 강의에서 나온 코드와 거의 흡사한데 채점을 하면 런타임 에러가 발생합니다. 무슨 문제일까요?

감사합니다.

import java.util.*;
import java.io.*;

class Main {
    static int N;
    static class Time implements Comparable<Time>{
        int time;
        char state;
        Time (int time, char state) {
            this.time = time;
            this.state = state;
        }
        @Override
	public int compareTo(Time ob){
		if(this.time==ob.time) return this.state-ob.state;
		else return this.time-ob.time;
	}
    }
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;
        N = Integer.parseInt(br.readLine());

        ArrayList<Time> guests = new ArrayList<>();
        for(int i = 0; i < N; i++) {
            st = new StringTokenizer(br.readLine());
            int start = Integer.parseInt(st.nextToken());
            int end = Integer.parseInt(st.nextToken());
            guests.add(new Time(start, 's'));
            guests.add(new Time(end, 'e'));
        }
        Collections.sort(guests);

        System.out.println(solution(guests));
    }

    public static int solution(ArrayList<Time> guests) {
        int ans = 0;
        int cnt = 0;
        for(Time t : guests) {
            if(t.state == 's') {
                cnt++;
                ans = Math.max(ans, cnt);
            } else {
                cnt--;
            }
        }
        return ans;
    }
}