urumqi-2017-online

存一個學姐用的模板(:з」∠)

因為每個點只能經過一次，拆點，限制為1
以上海為起點
大連和西安兩個點再連向終點，限制為1
判斷最終流量是否為2就能判斷是否從大連開始到西安結束了

#include<bits/stdc++.h>
using namespace std;
#define N 30005
#define M 60005
#define INF 10000000
#define ms(x,y) memset(x,y,sizeof(x))
const double EPS=1e-9;
struct Edge{
    int u,v,cap,next;
    double
 
 cost;
}edge[M<<1];
int sumFlow,edgeNum,head[N],pp[N];
double dist[N];
bool inq[N];
void add(int u,int v,int cap,double cost){
    edge[edgeNum].u=u;edge[edgeNum].v=v;edge[edgeNum].cap=cap;edge[edgeNum].cost=cost;
    edge[edgeNum].next=head[u];head[u]=edgeNum++;
    edge[edgeNum].u=v;edge[edgeNum].v=u;edge[edgeNum].cap=0
 
;edge[edgeNum].cost=-cost;
    edge[edgeNum].next=head[v];head[v]=edgeNum++;
}
bool SPFA(int s,int t,int n){
    int i,u,v;
    queue<int>q;
    ms(inq,0),ms(pp,-1);
    for(i=0;i<=n;i++) dist[i]=INF;
    inq[s]=1;dist[s]=0;
    q.push(s);
    while(!q.empty()){
        u=q.front();q.pop();inq[u]=0
 
;
        for(i=head[u];i!=-1;i=edge[i].next){
            v=edge[i].v;
            if(edge[i].cap&&dist[v]>dist[u]+edge[i].cost+EPS){
                dist[v]=dist[u]+edge[i].cost;
                pp[v]=i;
                if(!inq[v]){
                    q.push(v);
                    inq[v]=1;
                }
            }
        }
    }
    if(pp[t]==-1) return false;
    return true;
}
pair<int,double> MCMF(int s,int t,int n){
    int flow=0,i,minflow;
    double mincost=0;
    while(SPFA(s,t,n)){
        minflow=INF;
        for(i=pp[t];i!=-1;i=pp[edge[i].u])
            minflow=min(edge[i].cap,minflow);
        flow+=minflow;
        for(i=pp[t];i!=-1;i=pp[edge[i].u])
            edge[i].cap-=minflow,edge[i^1].cap+=minflow;
        mincost+=dist[t]*minflow;
    }
    return make_pair(flow,mincost);
}

map<string,int>MP;
int main()
{
    int t,n,m,i,u[N],v[N],w[N];
    scanf("%d",&t);
    while(t--){
        edgeNum=0,ms(head,-1);

        MP.clear();
        MP["Shanghai"]=1;
        MP["Dalian"]=2;
        MP["Xian"]=n=3;

        scanf("%d",&m);
        string s;
        for(i=1;i<=m;i++){
            cin>>s;
            if(MP.find(s)==MP.end()) MP[s]=++n;
            u[i]=MP[s];
            cin>>s;
            if(MP.find(s)==MP.end()) MP[s]=++n;
            v[i]=MP[s];
            scanf("%d",&w[i]);
        }
        for(i=1;i<=m;i++)
            if(u[i]==1) add(u[i],v[i],1,w[i]);
            else if (v[i]==1) add(v[i],u[i],1,w[i]);
            else add(u[i]+n-1,v[i],1,w[i]),add(v[i]+n-1,u[i],1,w[i]);

       // add(0,1,2,0);
        for(i=2;i<=n;i++) add(i,i+n-1,1,0);
        add(2+n-1,2*n,1,0);
        add(3+n-1,2*n,1,0);

        pair<int,double> p=MCMF(1,2*n,2*n);
        if(p.first==2) printf("%.0f\n",p.second);
        else puts("-1");
    }
}