题解 | 小sun的假期

#include <iostream>
#include <map>
using namespace std;

int main() {
    long long n, m;
    cin >> n >> m;
    map<long long, int> events;

    for (int i = 0; i < m; ++i) {
        long long l, r;
        cin >> l >> r;
        events[l]++;
        events[r + 1]--;
    }

    long long max_happiness = 0;
    long long current_coverage = 0;
    long long last_time = 1;

    for (auto& [time, delta] : events) {
        if (current_coverage == 0) {
            max_happiness = max(max_happiness, time - last_time);
        }
        current_coverage += delta;
        last_time = time;
    }

    // 处理末尾区间
    if (current_coverage == 0) {
        max_happiness = max(max_happiness, n - last_time + 1);
    }

    cout << max_happiness << endl;
    return 0;
}