[JZOJ] 5934. 列队

二分图棋盘模型，行列连边，求出最大独立集

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
 
using namespace std;
 
inline int rd(){
  int ret=0,f=1;char c;
  while(c=getchar(),!isdigit(c))f=c=='-'?-1:1;
  while(isdigit(c))ret=ret*10+c-'0',c=getchar();
  return ret*f;
}
#define space() putchar(' ')
#define nextline() putchar('
')
void pot(int x){if(!x)return;pot(x/10);putchar('0'+x%10);}
void out(int x){if(!x)putchar('0');if(x<0)putchar('-'),x=-x;pot(x);}
 
const int MAXN = 2005;
const int INF = 1<<30;
 
 int n,m;
 
int nex[MAXN*MAXN],to[MAXN*MAXN],fl[MAXN*MAXN];
int head[MAXN],ecnt=1;
inline void adds(int x,int y,int f){
    nex[++ecnt]=head[x];to[ecnt]=y;
    fl[ecnt]=f;head[x]=ecnt;
}
inline void add(int x,int y,int f){
    adds(x,y,f);adds(y,x,0);    
}
 
int dep[MAXN];
queue<int> Q;
bool bfs(int s,int t){
    memset(dep,0,sizeof(dep));
    Q.push(s);dep[s]=1;
    while(!Q.empty()){
        int top=Q.front();Q.pop();  
        for(int i=head[top];i;i=nex[i]){
            int v=to[i];
            if(dep[v]||fl[i]==0) continue;
            dep[v]=dep[top]+1;
            Q.push(v);  
        }
    }
    return dep[t];
}
int cur[MAXN];
int dfs(int x,int flow,int t){
    if(x==t) return flow;
    int tmp,used=0;
    for(int &i=cur[x];i;i=nex[i]){
        int v=to[i];
        if(dep[v]!=dep[x]+1)continue;
        tmp=dfs(v,min(flow-used,fl[i]),t);
        used+=tmp;fl[i]-=tmp;fl[i^1]+=tmp;
        if(used==flow) return flow; 
    }
    if(!used) dep[x]=-1;
    return used;
}
int dinic(int s,int t){
    int ret=0;
    while(bfs(s,t)){
        memcpy(cur,head,sizeof(head));
        ret+=dfs(s,INF,t);  
    }
    return ret;
}

bool vis[MAXN*MAXN];

int main(){
	freopen("phalanx.in","r",stdin);
	freopen("phalanx.out","w",stdout);
    n=rd();m=rd();
    int S=n+n+1,T=n+n+2;
    int x,y;
    for(int i=1;i<=n;i++) add(S,i,1);
    for(int i=1;i<=n;i++) add(i+n,T,1);
    for(int i=1;i<=m;i++){
    	x=rd();y=rd();
    	add(x,y+n,1);
    }
    cout<<2*n*n-n*dinic(S,T)<<endl; 
    return 0;
}