题解 | #剩下的树#

#include<iostream>
#include<cstdio>

using namespace std;

#define max 100000
    int main(){
        int road[max]={0};
        int l,m;
        int number=0;
        while(scanf("%d%d",&l,&m)!=EOF){
            for(int i=0;i<=l;i++)
                road[i]=1;
            while(m--){
                int left,right;
                scanf("%d%d",&left,&right);
                for(int j=left;j<=right;j++)
                road[j]=0;
            }
        for(int k=0;k<=l;k++)
        if(road[k]>0)
        number++;
        }
        printf("%d",number);
        return 0;
    }