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  • Dinic最大流模版

    struct Edge{
        int from,to,cap,flow;
    };
    bool cmp(const Edge& a,const Edge& b){
        return a.from < b.from || (a.from == b.from && a.to < b.to);
    }
    struct Dinic{
        int n,m,s,t;
        vector<Edge> edges;
        vector<int> G[MAXN];
        bool vis[MAXN];
        int d[MAXN];
        int cur[MAXN];
        void init(int n){
            this->n=n;
            for(int i=0;i<=n;i++)G[i].clear();
            edges.clear();
        }
        void AddEdge(int from,int to,int cap){
            edges.push_back((Edge){from,to,cap,0});
            edges.push_back((Edge){to,from,0,0});//当是无向图时,反向边容量也是cap,有向边时,反向边容量是0
            m=edges.size();
            G[from].push_back(m-2);
            G[to].push_back(m-1);
        }
        bool BFS(){
            CL(vis,0);
            queue<int> Q;
            Q.push(s);
            d[s]=0;
            vis[s]=1;
            while(!Q.empty()){
                int x=Q.front();
                Q.pop();
                for(int i=0;i<G[x].size();i++){
                    Edge& e=edges[G[x][i]];
                    if(!vis[e.to]&&e.cap>e.flow){
                        vis[e.to]=1;
                        d[e.to]=d[x]+1;
                        Q.push(e.to);
                    }
                }
            }
            return vis[t];
        }
        int DFS(int x,int a){
            if(x==t||a==0)return a;
            int flow=0,f;
            for(int& i=cur[x];i<G[x].size();i++){
                Edge& e=edges[G[x][i]];
                if(d[x]+1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0){
                    e.flow+=f;
                    edges[G[x][i]^1].flow-=f;
                    flow+=f;
                    a-=f;
                    if(a==0)break;
                }
            }
            return flow;
        }
        //当所求流量大于need时就退出,降低时间
        int Maxflow(int s,int t,int need){
            this->s=s;this->t=t;
            int flow=0;
            while(BFS()){
                CL(cur,0);
                flow+=DFS(s,INF);
                if(flow>need)return flow;
            }
            return flow;
        }
        //最小割割边
        vector<int> Mincut(){
            BFS();
            vector<int> ans;
            for(int i=0;i<edges.size();i++){
                Edge& e=edges[i];
                if(vis[e.from]&&!vis[e.to]&&e.cap>0)ans.push_back(i);
            }
            return ans;
        }
        void Reduce(){
            for(int i = 0; i < edges.size(); i++) edges[i].cap -= edges[i].flow;
        }
        void ClearFlow(){
            for(int i = 0; i < edges.size(); i++) edges[i].flow = 0;
        }
    };
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  • 原文地址:https://www.cnblogs.com/arbitrary/p/2941085.html
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