题解 | #剩下的树#

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

int main() {
    int l,m;
    cin>>l>>m;
    bool road[l+1];
    memset(road,true,sizeof(road));
    while(m>0){
        m--;
        int left,right;
        cin>>left>>right;
        for(int i=left;i<=right;i++){
            road[i]=false;
        }
    }
    int num=0;
    for(int i=0;i<=l;i++){
            if(road[i]) num++;
    }
    cout<<num<<endl;
}