POJ1459--Power Network(最大流)

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最大流模版题。多源点多汇点，只需再添加两个点，将其中一个点与各个源点连接，并将其最为源点，汇点同理。

#include <stdio.h>#include <iostream>#include <string>#include <algorithm>#include <math.h>#include <vector>#include <queue>using namespace std;const int maxn=205*205;const int INF=999999999;struct Edge{int from,to,cap,flow;};int n,m,s,t;vector<Edge> edges;vector<int> G[maxn];bool vis[maxn];int d[maxn];int cur[maxn];void init(){for(int i=0;i<maxn;i++)G[i].clear();memset(vis,0,sizeof(vis));memset(d,0,sizeof(d));memset(cur,0,sizeof(cur));}bool BFS(){memset(vis,0,sizeof(vis));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;}int Maxflow(int s,int t){int flow=0;while(BFS()){memset(cur,0,sizeof(cur));flow+=DFS(s,INF);}return flow;}void AddEdge(int from,int to,int cap){struct Edge e;e.from=from,e.to=to,e.cap=cap,e.flow=0;edges.push_back(e);e.from=to,e.to=from,e.cap=0,e.flow=0;edges.push_back(e);m=edges.size();G[from].push_back(m-2);G[to].push_back(m-1);}int main(){int np,nc,k;while(scanf("%d%d%d%d",&n,&np,&nc,&k)!=EOF){int u,v,l;char ch;init();for(int i=0;i<k;i++){cin>>ch>>u>>ch>>v>>ch>>l;AddEdge(u+1,v+1,l);}for(int i=0;i<np;i++){cin>>ch>>v>>ch>>l;AddEdge(0,v+1,l);}for(int i=0;i<nc;i++){cin>>ch>>u>>ch>>l;AddEdge(u+1,n+1,l);}s=0,t=n+1;int ans=Maxflow(s,t);printf("%d\n",ans);}return 0;}

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