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。
1 #include<cstdio> 2 #include<cstring> 3 #include<queue> 4 #include<algorithm> 5 using namespace std; 6 #define INF (1LL<<60) 7 #define MAXN 1111 8 #define MAXM 1111*1111*2 9 10 struct Edge{ 11 int v,next; 12 long long cap,flow; 13 }edge[MAXM]; 14 int vs,vt,NE,NV; 15 int head[MAXN]; 16 17 void addEdge(int u,int v,long long cap){ 18 edge[NE].v=v; edge[NE].cap=cap; edge[NE].flow=0; 19 edge[NE].next=head[u]; head[u]=NE++; 20 edge[NE].v=u; edge[NE].cap=0; edge[NE].flow=0; 21 edge[NE].next=head[v]; head[v]=NE++; 22 } 23 24 int level[MAXN]; 25 int gap[MAXN]; 26 void bfs(){ 27 memset(level,-1,sizeof(level)); 28 memset(gap,0,sizeof(gap)); 29 level[vt]=0; 30 gap[level[vt]]++; 31 queue<int> que; 32 que.push(vt); 33 while(!que.empty()){ 34 int u=que.front(); que.pop(); 35 for(int i=head[u]; i!=-1; i=edge[i].next){ 36 int v=edge[i].v; 37 if(level[v]!=-1) continue; 38 level[v]=level[u]+1; 39 gap[level[v]]++; 40 que.push(v); 41 } 42 } 43 } 44 45 int pre[MAXN]; 46 int cur[MAXN]; 47 long long ISAP(){ 48 bfs(); 49 memset(pre,-1,sizeof(pre)); 50 memcpy(cur,head,sizeof(head)); 51 int u=pre[vs]=vs; 52 long long flow=0,aug=INF; 53 gap[0]=NV; 54 while(level[vs]<NV){ 55 bool flag=false; 56 for(int &i=cur[u]; i!=-1; i=edge[i].next){ 57 int v=edge[i].v; 58 if(edge[i].cap!=edge[i].flow && level[u]==level[v]+1){ 59 flag=true; 60 pre[v]=u; 61 u=v; 62 //aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap)); 63 aug=min(aug,edge[i].cap-edge[i].flow); 64 if(v==vt){ 65 flow+=aug; 66 for(u=pre[v]; v!=vs; v=u,u=pre[u]){ 67 edge[cur[u]].flow+=aug; 68 edge[cur[u]^1].flow-=aug; 69 } 70 //aug=-1; 71 aug=INF; 72 } 73 break; 74 } 75 } 76 if(flag) continue; 77 int minlevel=NV; 78 for(int i=head[u]; i!=-1; i=edge[i].next){ 79 int v=edge[i].v; 80 if(edge[i].cap!=edge[i].flow && level[v]<minlevel){ 81 minlevel=level[v]; 82 cur[u]=i; 83 } 84 } 85 if(--gap[level[u]]==0) break; 86 level[u]=minlevel+1; 87 gap[level[u]]++; 88 u=pre[u]; 89 } 90 return flow; 91 } 92 int n; 93 long long G[555][555],d[555]; 94 bool vis[555]; 95 void SPFA(){ 96 for(int i=1; i<=n; ++i) d[i]=INF,vis[i]=0; 97 d[1]=0; vis[1]=1; 98 queue<int> que; 99 que.push(1); 100 while(!que.empty()){ 101 int u=que.front(); que.pop(); 102 for(int v=1; v<=n; ++v){ 103 if(G[u][v]==-1) continue; 104 if(d[v]>d[u]+G[u][v]){ 105 d[v]=d[u]+G[u][v]; 106 if(!vis[v]){ 107 vis[v]=1; 108 que.push(v); 109 } 110 } 111 } 112 vis[u]=0; 113 } 114 } 115 int main(){ 116 memset(G,-1,sizeof(G)); 117 int m,a,b,c; 118 scanf("%d%d",&n,&m); 119 while(m--){ 120 scanf("%d%d%d",&a,&b,&c); 121 if(G[a][b]==-1 || G[a][b]>c) G[b][a]=G[a][b]=c; 122 } 123 for(int i=1; i<=n; ++i) G[i][i]=0; 124 SPFA(); 125 vs=1; vt=n+n; NV=vt+1; NE=0; 126 memset(head,-1,sizeof(head)); 127 for(int i=1; i<=n; ++i){ 128 scanf("%d",&a); 129 if(i==1 || i==n) addEdge(i,i+n,INF); 130 else addEdge(i,i+n,a); 131 } 132 for(int i=1; i<=n; ++i){ 133 for(int j=1; j<=n; ++j){ 134 if(G[i][j]==-1 || i==j || d[i]==INF || d[j]==INF) continue; 135 if(d[i]+G[i][j]==d[j]) addEdge(i+n,j,INF); 136 } 137 } 138 printf("%lld",ISAP()); 139 return 0; 140 }
