poj 2391 Ombrophobic Bovines 二分+最大流
2015-04-20 11:51
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同poj 2112.
代码:
代码:
//poj 2391 //sep9 #include <iostream> #include <queue> #include <algorithm> using namespace std; typedef long long ll; const int maxN=1024; const int maxM=100002; const ll MAX=(1ULL<<63)-1; struct Edge { int v,f,nxt; }e[maxM*2+10]; queue<int> que; int src,sink; int g[maxN+10]; int nume; bool vis[maxN+10]; int dist[maxN+10]; ll d[maxN][maxN]; int in[maxN],out[maxN]; int f,p,sum; void addedge(int u,int v,int c) { e[++nume].v=v;e[nume].f=c;e[nume].nxt=g[u];g[u]=nume; e[++nume].v=u;e[nume].f=0;e[nume].nxt=g[v];g[v]=nume; } void init() { memset(g,0,sizeof(g)); nume=1; } int bfs() { while(!que.empty()) que.pop(); memset(dist,0,sizeof(dist)); memset(vis,0,sizeof(vis)); vis[src]=true; que.push(src); while(!que.empty()){ int u=que.front();que.pop(); for(int i=g[u];i;i=e[i].nxt) if(e[i].f&&!vis[e[i].v]){ que.push(e[i].v); dist[e[i].v]=dist[u]+1; vis[e[i].v]=true; if(e[i].v==sink) return 1; } } return 0; } int dfs(int u,int delta) { if(u==sink) return delta; int ret=0; for(int i=g[u];ret<delta&&i;i=e[i].nxt) if(e[i].f&&dist[e[i].v]==dist[u]+1){ int dd=dfs(e[i].v,min(e[i].f,delta-ret)); if(dd>0){ e[i].f-=dd; e[i^1].f+=dd; ret+=dd; } else dist[e[i].v]=-1; } return ret; } int dinic() { int ret=0; while(bfs()==1) ret+=dfs(src,INT_MAX); return ret; } bool work(ll max_len) { init(); src=0,sink=2*f+1; for(int i=1;i<=f;++i) addedge(src,i,in[i]); for(int i=1;i<=f;++i) for(int j=1;j<=f;++j) if(d[i][j]<=max_len) addedge(i,j+f,INT_MAX); for(int j=f+1;j<=2*f;++j) addedge(j,sink,out[j-f]); if(dinic()==sum) return true; return false; } int main() { scanf("%d%d",&f,&p); for(int i=1;i<=f;++i){ for(int j=1;j<=f;++j) d[i][j]=d[j][i]=MAX; d[i][i]=0; } sum=0; for(int i=1;i<=f;++i){ scanf("%d%d",&in[i],&out[i]); sum+=in[i]; } while(p--){ int a,b; ll c; scanf("%d%d%I64d",&a,&b,&c); c=min(d[a][b],c); d[a][b]=d[b][a]=c; } for(int k=1;k<=f;++k) for(int i=1;i<=f;++i) for(int j=1;j<=f;++j) if(d[i][k]!=MAX&&d[k][j]!=MAX) d[i][j]=min(d[i][j],d[i][k]+d[k][j]); ll l=0,r=MAX/2,mid,ans=-1; while(l<r){ mid=(l+r)/2; if(work(mid)){ ans=mid; r=mid; }else l=mid+1; } printf("%I64d",ans); return 0; }
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