UVa10806 Dijkstra,Dijkstra-费用网络流

Problem, in short Given a weighed, undirected graph, find the shortest path from S to T and back without using the same edge twice.

很基础的费用网络流

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<queue>
 #include<vector>
 #define LL long long
 #define maxn 1024
 using namespace std;
 <<;
 struct Edge{
     int from,to,dist,flow,cap;
 };
 int n,m,d[maxn],a[maxn],inq[maxn],p[maxn];
 vector<Edge> edges;
 vector<int> G[maxn];
 void addEdge(int from,int to,int dist){
     edges.push_back((Edge){,});
     edges.push_back((Edge){to,,});
     int m=edges.size();
     G[);
     G[to].push_back(m-);
 }
 void connect(){
     edges.push_back((Edge){,n+,,,});
     edges.push_back((Edge){n+,,,,});
     int m=edges.size();
     G[].push_back(m-);
     G[n+].push_back(m-);
     edges.push_back((Edge){n+,,,,});
     edges.push_back((Edge){,n+,,,});
     m+=;
     G[n+].push_back(m-);
     G[].push_back(m-);
     edges.push_back((Edge){n,n+,,,});
     edges.push_back((Edge){n+,n,,,});
     m+=;
     G[n].push_back(m-);
     G[n+].push_back(m-);
     edges.push_back((Edge){n+,n,,,});
     edges.push_back((Edge){n,n+,,,});
     m+=;
     G[n+].push_back(m-);
     G[n].push_back(m-);
 }
 bool BF(int s,int t,int &flow,int &cost){
     memset(inq,,sizeof(inq));
     ;i<=n+;i++) d[i]=inf;
     inq[s]=;d[s]=;a[s]=inf;
     queue<int> Q;
     Q.push(s);
     while(!Q.empty()){
         int u=Q.front();Q.pop();
         inq[u]=;
         ;i<G[u].size();i++){
             Edge &e=edges[G[u][i]];
             if(e.cap>e.flow&&d[e.to]>d[u]+e.dist){
                 d[e.to]=d[u]+e.dist;
                 a[e.to]=min(a[u],e.cap-e.flow);
                 p[e.to]=G[u][i];
                 if(!inq[e.to]){
                     inq[e.to]=;
                     Q.push(e.to);
                 }
             }
         }
     }
     if(d[t]>=inf) return false;
     flow+=a[t];
     cost+=a[t]*d[t];
     int u=t;
     for(;u!=s;u=edges[p[u]].from){
         edges[p[u]].flow+=a[t];
         edges[p[u]^].flow-=a[t];
     }
     return true;
 }
 void init(){
     edges.clear();
     ;i<=n+;i++) G[i].clear();
 }
 int main()
 {
     while(scanf("%d",&n)&&n){
         scanf("%d",&m);
         init();
         int x,y,d;
         ;i<=m;i++){
             scanf("%d%d%d",&x,&y,&d);
             addEdge(x,y,d);addEdge(y,x,d);
         }
         connect();
         ,cost=;
         ,n+,flow,cost));
         ){
             puts("Back to jail");
         }else{
             printf("%d\n",cost);
         }
     }
     ;
 }