BZOJ3931 [CQOI2015]网络吞吐量（最大流）

没啥好说的，有写过类似的，就是预处理出最短路上的边建容量网络。

 #include<cstdio>
 #include<cstring>
 #include<queue>
 #include<algorithm>
 using namespace std;
 #define INF (1LL<<60)
 #define MAXN 1111
 #define MAXM 1111*1111*2

 struct Edge{
     int v,next;
     long long cap,flow;
 }edge[MAXM];
 int vs,vt,NE,NV;
 int head[MAXN];

 void addEdge(int u,int v,long long cap){
     edge[NE].v=v; edge[NE].cap=cap; edge[NE].flow=;
     edge[NE].next=head[u]; head[u]=NE++;
     edge[NE].v=u; edge[NE].cap=; edge[NE].flow=;
     edge[NE].next=head[v]; head[v]=NE++;
 }

 int level[MAXN];
 int gap[MAXN];
 void bfs(){
     memset(level,-,sizeof(level));
     memset(gap,,sizeof(gap));
     level[vt]=;
     gap[level[vt]]++;
     queue<int> que;
     que.push(vt);
     while(!que.empty()){
         int u=que.front(); que.pop();
         for(int i=head[u]; i!=-; i=edge[i].next){
             int v=edge[i].v;
             if(level[v]!=-) continue;
             level[v]=level[u]+;
             gap[level[v]]++;
             que.push(v);
         }
     }
 }

 int pre[MAXN];
 int cur[MAXN];
 long long ISAP(){
     bfs();
     memset(pre,-,sizeof(pre));
     memcpy(cur,head,sizeof(head));
     int u=pre[vs]=vs;
     long long flow=,aug=INF;
     gap[]=NV;
     while(level[vs]<NV){
         bool flag=false;
         for(int &i=cur[u]; i!=-; i=edge[i].next){
             int v=edge[i].v;
             if(edge[i].cap!=edge[i].flow && level[u]==level[v]+){
                 flag=true;
                 pre[v]=u;
                 u=v;
                 //aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap));
                 aug=min(aug,edge[i].cap-edge[i].flow);
                 if(v==vt){
                     flow+=aug;
                     for(u=pre[v]; v!=vs; v=u,u=pre[u]){
                         edge[cur[u]].flow+=aug;
                         edge[cur[u]^].flow-=aug;
                     }
                     //aug=-1;
                     aug=INF;
                 }
                 break;
             }
         }
         if(flag) continue;
         int minlevel=NV;
         for(int i=head[u]; i!=-; i=edge[i].next){
             int v=edge[i].v;
             if(edge[i].cap!=edge[i].flow && level[v]<minlevel){
                 minlevel=level[v];
                 cur[u]=i;
             }
         }
         if(--gap[level[u]]==) break;
         level[u]=minlevel+;
         gap[level[u]]++;
         u=pre[u];
     }
     return flow;
 }
 int n;
 long long G[][],d[];
 bool vis[];
 void SPFA(){
     for(int i=; i<=n; ++i) d[i]=INF,vis[i]=;
     d[]=; vis[]=;
     queue<int> que;
     que.push();
     while(!que.empty()){
         int u=que.front(); que.pop();
         for(int v=; v<=n; ++v){
             if(G[u][v]==-) continue;
             if(d[v]>d[u]+G[u][v]){
                 d[v]=d[u]+G[u][v];
                 if(!vis[v]){
                     vis[v]=;
                     que.push(v);
                 }
             }
         }
         vis[u]=;
     }
 }
 int main(){
     memset(G,-,sizeof(G));
     int m,a,b,c;
     scanf("%d%d",&n,&m);
     while(m--){
         scanf("%d%d%d",&a,&b,&c);
         if(G[a][b]==- || G[a][b]>c) G[b][a]=G[a][b]=c;
     }
     for(int i=; i<=n; ++i) G[i][i]=;
     SPFA();
     vs=; vt=n+n; NV=vt+; NE=;
     memset(head,-,sizeof(head));
     for(int i=; i<=n; ++i){
         scanf("%d",&a);
         if(i== || i==n) addEdge(i,i+n,INF);
         else addEdge(i,i+n,a);
     }
     for(int i=; i<=n; ++i){
         for(int j=; j<=n; ++j){
             if(G[i][j]==- || i==j || d[i]==INF || d[j]==INF) continue;
             if(d[i]+G[i][j]==d[j]) addEdge(i+n,j,INF);
         }
     }
     printf("%lld",ISAP());
     return ;
 }