HDU3488 Cyclic Tour(有向环最小覆盖)
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思路:和hdu1853几乎一样的代码和思路...
#include<cstdio>#include<cstring>#include<algorithm>#include<queue>#include<vector>#define INF 1e9using namespace std;const int maxn=400+5;struct Edge{ int from,to,cap,flow,cost; Edge(){} Edge(int f,int t,int c,int fl,int co):from(f),to(t),cap(c),flow(fl),cost(co){}};struct MCMF{ int n,m,s,t; vector<Edge> edges; vector<int> G[maxn]; bool inq[maxn]; int d[maxn]; int p[maxn]; int a[maxn]; void init(int n,int s,int t) { this->n=n, this->s=s, this->t=t; edges.clear(); for(int i=0;i<n;++i) G[i].clear(); } void AddEdge(int from,int to,int cap,int cost) { edges.push_back(Edge(from,to,cap,0,cost)); edges.push_back(Edge(to,from,0,0,-cost)); m=edges.size(); G[from].push_back(m-2); G[to].push_back(m-1); } bool BellmanFord(int &flow,int &cost) { queue<int> Q; for(int i=0;i<n;++i) d[i]=INF; memset(inq,0,sizeof(inq)); Q.push(s),inq[s]=true,d[s]=0,a[s]=INF,p[s]=0; while(!Q.empty()) { int u=Q.front(); Q.pop(); inq[u]=false; for(int i=0;i<G[u].size();++i) { Edge &e=edges[G[u][i]]; if(e.cap>e.flow && d[e.to]>d[u]+e.cost) { d[e.to]=d[u]+e.cost; a[e.to]=min(a[u],e.cap-e.flow); p[e.to]=G[u][i]; if(!inq[e.to]){inq[e.to]=true; Q.push(e.to);} } } } if(d[t]==INF) return false; flow += a[t]; cost += a[t]*d[t]; int u=t; while(u!=s) { edges[p[u]].flow +=a[t]; edges[p[u]^1].flow -=a[t]; u=edges[p[u]].from; } return true; } int solve(int num) { int flow=0,cost=0; while(BellmanFord(flow,cost)); return flow==num?cost:-1; }}MM;int main(){ int T;scanf("%d",&T); while(T--) { int n,m; scanf("%d%d",&n,&m); int src=0,dst=2*n+1; MM.init(2*n+2,src,dst); for(int i=1;i<=n;++i) { MM.AddEdge(src,i,1,0); MM.AddEdge(i+n,dst,1,0); } while(m--) { int u,v,w; scanf("%d%d%d",&u,&v,&w); MM.AddEdge(u,v+n,1,w); } printf("%d\n",MM.solve(n)); } return 0;}
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