题解 | 小sun的假期

#include<bits/stdc++.h>
using namespace std;
#define int long long
void solve()
{
    int n,m;
    cin>>n>>m;
    map<int,int>mp;
    for(int i=1;i<=m;i++)
    {
        int l,r;
        cin>>l>>r;
        mp[l]++,mp[r+1]--;
    }
    int now=0;
    int maxn=0,pre=0;
    for(auto&pair:mp)
    {
        if(now==0)
        {
            maxn=max(maxn,pair.first-pre);

        }
        now+=pair.second;
        if(now==0)pre=pair.first;
    }
    if(now==0)
    {
        maxn=max(maxn,n+1-pre);
    }
    cout<<maxn<<"\n";
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    int t=1;
    //cin>>t;
    while(t--)
    {
        solve();
    }
    return 0;
}