题解 | #剩下的树#

#include <algorithm>
#include<bits/stdc++.h>
using namespace std;

#define MAX 10001

bool flag[MAX] = {false};

int main() {
    int len;
    int m;
    cin >> len;
    while(cin >> m) {
        int a, b;
        for(int i = 0; i < m; i++) {
            cin >> a >> b;
            int left = min(a,b);
            int right = max(a,b);
            for(int i = left; i <= right; i++) {
                flag[i] = true;
            }
        }
    }
    int sum = 0;
    for(int i = 0; i <= len; i++) {
        if(flag[i] == false) {
            sum++;
        }
    }
    cout << sum << endl;
}