题解 | 校门外的树

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

int main() {
    int l,m;
    cin>>l>>m;
    vector<int> a(l+1,1);
    int x1,x2;
    int sum=0;
    while(m>0){
        cin>>x1>>x2;
        for(int i=x1;i<x2+1;i++){
            a[i]=0;
        }
        m--;
    }
    int count=0;
    for(int i=0;i<=l+1;i++){
        if(a[i]!=0){
            count++;
        }
    }
    cout<<count;
}