大佬们看看这个我2和3的测试点会多1。

#include<bits/stdc++.h>
using namespace std;
int n,m,x,y,i,j,a[10000],sum,t;
int main()
{
    //freopen("tree.in","r",stdin);
    //freopen("tree.out","w",stdout);
    scanf("%d%d",&n,&m);
    sum=n+1;
    for (i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        if (x>y) 
        {
            t=x; x=y; y=t;
        }
        for (j=x;j<=y;j++)
        if (a[j]==0)    
        {
            a[j]=1;
            sum--;
        }
    }
    printf("%d",sum);
    return 0;
}