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\n",Mincost(0,n+1));

    }

    return 0;

}