poj 1273Drainage Ditches(简单网络流（用dinic）)

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//poj 1273Drainage Ditches(简单网络流（用dinic）)#include<iostream>#include<cstdio>#include<vector>#include<string.h>#include<queue>using namespace std;const int N=500;const int INF=1<<30;int Min(int a,int b){return a<b?a:b;}//==============邻接表==================struct Edge{    int from,to,cap,flow;};struct Dinic{    int start,end,n,m;    vector<Edge> edges;    vector<int> G[N];//邻接表    void AddEdge(int from,int to,int cap)   {       Edge e;       e.from=from;e.cap=cap;e.to=to;e.flow=0;       edges.push_back(e);       e.from=to;e.cap=0;e.to=from;e.flow=0;       edges.push_back(e);       int m1=edges.size();       G[from].push_back(m1-2);       G[to].push_back(m1-1);   }//===============================   int vis[N];   int d[N];   int cur[N];//=========分层次==================   bool BFS()   {       memset(vis,0,sizeof(vis));       queue<int> q;       q.push(start);       d[start]=0;       vis[start]=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[end];    }//===============================    int DFS(int x,int a)    {        if(x==end||a==0) return a;        int flow=0,f;        for(int i=0;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;    }    int Maxflow(int s,int t)    {        start=s;end=t;        int flow=0;        while(BFS())        {            memset(cur,0,sizeof(cur));            flow+=DFS(s,INF);        }        return flow;    }};int main(){    Dinic flo,te;    while(scanf("%d%d",&flo.m,&flo.n)!=EOF)    {        int a,b,c;        for(int i=0;i<flo.m;i++)        {            scanf("%d%d%d",&a,&b,&c);            flo.AddEdge(a,b,c);        }        printf("%d\n",flo.Maxflow(1,flo.n));        flo=te;        //cout<<INF<<endl;    }    return 0;}
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