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    inf开太小错了好久……下次还是要用0x7fffffff

    #include<stdio.h>
    #include<string.h>
    #include<vector>
    #include<queue>
    #include<algorithm>
    using namespace std;
    const int N=5024;
    const int inf=0x7fffffff;
    struct Edge
    {
        int from,to,cap,flow,cost;
    };
    vector<Edge>edges;
    vector<int>G[N];
    int n,m;
    int inq[N],p[N],d[N],a[N];
    
    void AddEdge(int from, int to,int cap, int cost)
    {
        Edge tp;
        tp.from=from,tp.to=to,tp.cap=cap,tp.flow=0,tp.cost=cost;
        edges.push_back(tp);
    
        tp.from=to,tp.to=from,tp.cap=0,tp.flow=0,tp.cost=-cost;
        edges.push_back(tp);
    
        int g=edges.size();
        G[from].push_back(g-2);
        G[to].push_back(g-1);
    }
    
    int BellmanFord(int s,int t,int &flow, int &cost)
    {
        int i,j,u;
        for(i=0; i<=n+1; i++) d[i]=inf;
        memset(inq,0,sizeof(inq));
        d[s]=0;
        inq[s]=1;
        p[s]=0;
        a[s]=inf;
        queue<int>Q;
        Q.push(s);
        while(!Q.empty())
        {
            u=Q.front();
            Q.pop();
            inq[u]=0;
            for(i=0; i<G[u].size(); i++)
            {
                Edge &e=edges[G[u][i]];
                if(e.cap>e.flow&&d[e.to]>d[u]+e.cost)
                {
                    d[e.to]=d[u]+e.cost;
                    p[e.to]=G[u][i];
                    a[e.to]=min(a[u],e.cap-e.flow);
                    if(!inq[e.to])
                    {
                        Q.push(e.to);
                        inq[e.to]=1;
                    }
                }
            }
        }
        if(d[t]==inf) return 0;
        flow+=a[t];
        cost+=d[t]*a[t];
        u=t;
        while(u!=0)
        {
            edges[p[u]].flow+=a[t];
            edges[p[u]^1].flow-=a[t];
            u=edges[p[u]].from;
        }
        return 1;
    }
    
    int Mincost(int s,int t)
    {
        int flow=0,cost=0;
        while(BellmanFord(s,t,flow,cost));
        return cost;
    }
    
    int main()
    {
        int i,u,v,c;
        while(~scanf("%d%d",&n,&m))
        {
            for(i=0; i<=n+1; i++) G[i].clear();
            edges.clear();
            for(i=0;i<m;i++)
            {
                scanf("%d%d%d",&u,&v,&c);
                AddEdge(u,v,1,c);
                AddEdge(v,u,1,c);
            }
            AddEdge(0,1,2,0);
            AddEdge(n,n+1,2,0);
            printf("%d
    ",Mincost(0,n+1));
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/zhchoutai/p/8603853.html
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