Poj(2135)，MCMF，模板

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>

using namespace std;
int sumFlow;
const int MAXN = 1010;
const int MAXM = 1000200;
#define INF 0x3f3f3f3f

struct Edge
{
    int u;
    int v;
    int cap;
    int cost;
    int next;
} edge[MAXM<<2];

int NE;
int head[MAXN], dist[MAXN], pre[MAXN];
bool vis[MAXN];

void addedge(int u,int v,int cap,int cost)
{
    edge[NE].u=u;
    edge[NE].v=v;
    edge[NE].cap=cap;
    edge[NE].cost=cost;
    edge[NE].next=head[u];
    head[u]=NE++;

    edge[NE].u=v;       ///反的容量图
    edge[NE].v=u;
    edge[NE].cap=0;
    edge[NE].cost=-cost;
    edge[NE].next=head[v];
    head[v]=NE++;
}

bool SPFA(int s,int t,int n)
{
    int i,u,v;
    queue<int>Q;
    memset(vis,false,sizeof(vis));
    memset(pre,-1,sizeof(pre));
    for(i=0; i<=n; i++)
        dist[i]=INF;
    vis[s]=true;
    dist[s]=0;
    Q.push(s);
    while(!Q.empty())
    {
        u=Q.front();
        Q.pop();
        vis[u]=false;
        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)
            {
                dist[v]=dist[u]+edge[i].cost;
                pre[v]=i;
                if(!vis[v])
                {
                    Q.push(v);
                    vis[v]=true;
                }
            }
        }
    }
    if(dist[t]==INF)
        return false;
    return true;
}


int MCMF(int s,int t,int n)
{
    int flow=0; /// 总流量
    int minflow,mincost;
    mincost=0;
    while(SPFA(s,t,n))
    {
        minflow=INF+1;      ///容量瓶颈
        for(int i=pre[t]; i!=-1; i=pre[edge[i].u])
            if(edge[i].cap<minflow)
                minflow=edge[i].cap;
        flow+=minflow;
        for(int i=pre[t]; i!=-1; i=pre[edge[i].u])
        {
            edge[i].cap-=minflow;
            edge[i^1].cap+=minflow;     ///更新残余网络，^1处理，因为0,是正边，1是反边，做^1，就能找到反边
        }
        mincost+=dist[t]*minflow;       ///这里和书上有点不一样，就是相当于一个合并同类项了，dist[t]到汇点的最少花费*瓶颈容量
    }
    sumFlow=flow; /// 最大流
    return mincost;
}

int main()
{
    int n,m;
    int u,v,c;
    while(~scanf("%d%d",&n,&m))
    {
        NE=0;
        memset(head,-1,sizeof(head));
        int S=0;
        int T=n+1;
        while(m--)
        {
            scanf("%d%d%d",&u,&v,&c);
            addedge(u,v,1,c);
            addedge(v,u,1,c);   ///建反图，这样在SPFA里面就能回来了，
        }
        addedge(S,1,2,0);
        addedge(n,T,2,0);
        int ans=MCMF(S,T,T+1);
        printf("%d\n",ans);
    }
    return 0;
}