代码-SHOI2003 吃豆豆

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
#define x first
#define y second
#define bg begin()
#define ed end()
#define pb push_back
#define mp make_pair
#define sz(a) int((a).size())
#define R(i,n) for(int i(0);i<(n);++i)
#define L(i,n) for(int i((n)-1);~i;--i)
const int iinf=0x3f3f3f3f;
const ll linf=0x3f3f3f3f3f3f3f3f;

//Data
const int N=2000;
int n,f[N];
pair<int,int> a[N];
mt19937 orz(time(0));

//Flows
const int fN=4003;
int fn,s,t;
vector<int> e[fN],to,fw,co;
void adde(int u,int v,int w,int c){
    // cout<<u<<" "<<v<<" "<<w<<" "<<c<<'\n';
    e[u].pb(sz(to)),to.pb(v),fw.pb(w),co.pb(+c);
    e[v].pb(sz(to)),to.pb(u),fw.pb(0),co.pb(-c);
}
int dep[fN],pre[fN]; bool vis[fN];
bool spfa(){
    R(u,fn) dep[u]=iinf,pre[u]=-1,vis[u]=false;
    static queue<int> q; while(sz(q)) q.pop();
    q.push(s),dep[s]=0,vis[s]=true;
    while(sz(q)){
        int u=q.front(); q.pop(),vis[u]=false;
        for(int v:e[u])if(fw[v]&&dep[to[v]]>dep[u]+co[v])
            dep[to[v]]=dep[u]+co[v],pre[to[v]]=v,
            !vis[to[v]]&&(q.push(to[v]),vis[to[v]]=true);
    }
    return dep[t]<iinf;
}
pair<int,int> mcmf(){
    pair<int,int> res(0,0);
    while(spfa()){
        int f=iinf;
        for(int u=t;u^s;u=to[pre[u]^1]) f=min(f,fw[pre[u]]);
        for(int u=t;u^s;u=to[pre[u]^1]) fw[pre[u]]-=f,fw[pre[u]^1]+=f;
        res.x+=f,res.y+=dep[t]*f;
    }
    return res;
}

//Main
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    cin>>n,fn=(t=(s=(n<<1)+1)+1)+1;
    R(i,n) cin>>a[i].x>>a[i].y,f[i]=1;
    sort(a,a+n),adde(s,n<<1,2,0);
    R(i,n)R(j,i)if(a[j].y<=a[i].y) f[i]=max(f[i],f[j]+1);
    R(i,n)R(j,i)if(a[j].y<=a[i].y&&f[i]-f[j]<=98) adde(j+n,i,1,0);
    R(i,n) adde(i,i+n,1,-1),adde(n<<1,i,1,0),adde(i+n,t,1,0);
    cout<<-mcmf().y<<'\n';
    return 0;
}