BZOJ3931 [CQOI2015]网络吞吐量（最大流）

#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=0;
edge[NE].next=head[u]; head[u]=NE++;
edge[NE].v=u; edge[NE].cap=0; edge[NE].flow=0;
edge[NE].next=head[v]; head[v]=NE++;
}

int level[MAXN];
int gap[MAXN];
void bfs(){
memset(level,-1,sizeof(level));
memset(gap,0,sizeof(gap));
level[vt]=0;
gap[level[vt]]++;
queue<int> que;
que.push(vt);
while(!que.empty()){
int u=que.front(); que.pop();
for(int i=head[u]; i!=-1; i=edge[i].next){
int v=edge[i].v;
if(level[v]!=-1) continue;
level[v]=level[u]+1;
gap[level[v]]++;
que.push(v);
}
}
}

int pre[MAXN];
int cur[MAXN];
long long ISAP(){
bfs();
memset(pre,-1,sizeof(pre));
memcpy(cur,head,sizeof(head));
int u=pre[vs]=vs;
long long flow=0,aug=INF;
gap[0]=NV;
while(level[vs]<NV){
bool flag=false;
for(int &i=cur[u]; i!=-1; i=edge[i].next){
int v=edge[i].v;
if(edge[i].cap!=edge[i].flow && level[u]==level[v]+1){
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]^1].flow-=aug;
}
//aug=-1;
aug=INF;
}
break;
}
}
if(flag) continue;
int minlevel=NV;
for(int i=head[u]; i!=-1; 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]]==0) break;
level[u]=minlevel+1;
gap[level[u]]++;
u=pre[u];
}
return flow;
}
int n;
long long G[555][555],d[555];
bool vis[555];
void SPFA(){
for(int i=1; i<=n; ++i) d[i]=INF,vis[i]=0;
d[1]=0; vis[1]=1;
queue<int> que;
que.push(1);
while(!que.empty()){
int u=que.front(); que.pop();
for(int v=1; v<=n; ++v){
if(G[u][v]==-1) continue;
if(d[v]>d[u]+G[u][v]){
d[v]=d[u]+G[u][v];
if(!vis[v]){
vis[v]=1;
que.push(v);
}
}
}
vis[u]=0;
}
}
int main(){
memset(G,-1,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]==-1 || G[a][b]>c) G[b][a]=G[a][b]=c;
}
for(int i=1; i<=n; ++i) G[i][i]=0;
SPFA();
vs=1; vt=n+n; NV=vt+1; NE=0;
memset(head,-1,sizeof(head));
for(int i=1; i<=n; ++i){
scanf("%d",&a);
if(i==1 || i==n) addEdge(i,i+n,INF);
else addEdge(i,i+n,a);
}
for(int i=1; i<=n; ++i){
for(int j=1; j<=n; ++j){
if(G[i][j]==-1 || 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 0;
}