基础网络流学习笔记

以前太naive了，对着蓝书写vector存边，常数惊人。

今天拿链表重写了一遍。

话说把结果输出写到析构函数里好好玩，可以调戏同学：

“喂，你看啊，我的程序没输出喔~”

（掩面）

Dinic:

#include<cstdio>
#include<queue>

#define INF 0x3f3f3f3f
#define MAXN 10005
#define MAXM 100005

#define minn(a,b) ((a)<(b)?(a):(b))

int n,m;

struct Dinic{
    int s,t;
    
    int flow,cost;
    int cnt,head[MAXN],next[MAXM<<1|1];
    int dis[MAXN],cur[MAXN];
    
    std::queue<int> Q;
    
    struct Edge{
        int u,v,c,f;
        
        Edge(){}
        Edge(int u,int v,int c,int f):u(u),v(v),c(c),f(f){}
    }e[MAXM<<1|1];
    
    Dinic(){
        for(int i=0;i<MAXN;++i) head[i]=-1;
    }
    ~Dinic(){
        printf("%d
",flow);
    }
    
    inline void addedge(int u,int v,int c){
        e[cnt]=Edge(u,v,c,0);
        next[cnt]=head[u];
        head[u]=cnt++;
        
        e[cnt]=Edge(v,u,0,0);
        next[cnt]=head[v];
        head[v]=cnt++;
    }
    
    inline bool BFS(){
        for(int i=0;i<=n;++i) dis[i]=0;
        dis[s]=1,Q.push(s);
        
        while(Q.empty()==false){
            int u=Q.front();
            Q.pop();
            
            for(int i=head[u];i!=-1;i=next[i]){
                Edge &ed=e[i];
                
                if(ed.c>ed.f&&dis[ed.v]==0)
                    dis[ed.v]=dis[u]+1,Q.push(ed.v);
            }
        }
        
        return dis[t];
    }
    
    int DFS(int u,int res){
        if(u==t||res==0) return res;
        
        int fff=0;
        for(int &i=cur[u];i!=-1;i=next[i]){
            Edge &ed=e[i];
            
            if(ed.c>ed.f&&dis[u]+1==dis[ed.v]){
                int f=DFS(ed.v,minn(ed.c-ed.f,res));
                
                fff+=f,res-=f;
                ed.f+=f,e[i^1].f-=f;
                
                if(res==0) break;
            }
        }
        
        return fff;
    }
    
    void solve(){
        while(BFS()){
            for(int i=0;i<=n;++i) cur[i]=head[i];
            flow+=DFS(s,INF);
        }
    }
};

Dinic a;

int main(){
    scanf("%d%d%d%d",&n,&m,&a.s,&a.t);
    
    register int x,y,z;
    for(register int i=0;i<m;++i){
        scanf("%d%d%d",&x,&y,&z);
        a.addedge(x,y,z);
    }
    
    a.solve();
    
    return 0;
}

MCMF:

#include<cstdio>
#include<queue>

#define INF 0x3f3f3f3f
#define MAXN 5005
#define MAXM 50005

#define minn(a,b) ((a)<(b)?(a):(b))

int n,m;

struct MCMF{
    int s,t;
    
    int flow,cost;
    int cnt,head[MAXN],next[MAXM<<1|1];
    int dis[MAXN],res[MAXN],pre[MAXN];
    
    bool inq[MAXN];
    
    std::queue<int> Q;
    
    struct Edge{
        int u,v,c,f,cost;
        
        Edge(){}
        Edge(int u,int v,int c,int f,int cost):u(u),v(v),c(c),f(f),cost(cost){}
    }e[MAXM<<1|1];
    
    MCMF(){
        for(int i=0;i<=MAXN;++i) head[i]=-1;
    }
    ~MCMF(){
        printf("%d %d
",flow,cost);
    }
    
    inline void addedge(int u,int v,int c,int cost){
        e[cnt]=Edge(u,v,c,0,cost);
        next[cnt]=head[u];
        head[u]=cnt++;
        
        e[cnt]=Edge(v,u,0,0,-cost);
        next[cnt]=head[v];
        head[v]=cnt++;
    }
    
    inline bool SPFA(){
        for(int i=0;i<=n;++i) dis[i]=INF,inq[i]=false;
        dis[s]=0,inq[s]=true,res[s]=INF,Q.push(s);
        
        while(Q.empty()==false){
            int u=Q.front();
            Q.pop(),inq[u]=false;
            
            for(int i=head[u];i!=-1;i=next[i]){
                Edge &ed=e[i];
                
                if(ed.c>ed.f&&dis[ed.v]>dis[u]+ed.cost){
                    dis[ed.v]=dis[u]+ed.cost;
                    res[ed.v]=minn(ed.c-ed.f,res[u]);
                    pre[ed.v]=i;
                    
                    if(!inq[ed.v])
                        Q.push(ed.v),inq[ed.v]=true;
                }
            }
        }
        
        if(dis[t]==INF) return false;
        
        flow+=res[t];
        cost+=res[t]*dis[t];
        
        for(int u=t;u!=s;u=e[pre[u]].u){
            e[pre[u]].f+=res[t];
            e[pre[u]^1].f-=res[t];
        }
        
        return true;
    }
    
    inline void solve(){
        while(SPFA());
    }
};

MCMF a;

int main(){
    scanf("%d%d%d%d",&n,&m,&a.s,&a.t);
    
    register int u,v,c,cost;
    for(int i=1;i<=m;++i){
        scanf("%d%d%d%d",&u,&v,&c,&cost);
        a.addedge(u,v,c,cost);
    }
    
    a.solve();
    
    return 0;
}