HDOJ1853-费用流(圈,拆点)

//代码MCMF和SPFA部分直接拷贝来源于AOJ581
#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;

const int NN=250;
const int MM=50000;
const int INF=0x3fffffff;

struct Edge{
    int u,v,cost,flow,next;
}edge[MM];
int head[NN];
int n,m,S,T,NV,ecnt;

void init()
{
    S=0; T=2*n+1;
    NV=T+1;
    ecnt=1;
    for (int i=0; i<NV; i++) head[i]=0;
}

void addedge(int u,int v,int cost,int flow)
{
    ecnt++;
    edge[ecnt].u=u;
    edge[ecnt].v=v;
    edge[ecnt].cost=cost;
    edge[ecnt].flow=flow;
    edge[ecnt].next=head[u];
    head[u]=ecnt;
    ecnt++;
    edge[ecnt].u=v;
    edge[ecnt].v=u;
    edge[ecnt].cost=-cost;
    edge[ecnt].flow=0;
    edge[ecnt].next=head[v];
    head[v]=ecnt;
}


void build_graph()
{
    int x,y,z;
    for (int i=1; i<=n; i++)
    {
        addedge(S,i,0,1);
        addedge(i+n,T,0,1);
    }
    for (int i=1; i<=m; i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        addedge(x,y+n,z,1);
    }
}

bool used[NN];
int dis[NN],p[NN];
bool SPFA(void){
    queue<int> q;
    for (int i=1; i<NV; i++) dis[i]=INF;
    dis[S]=0;
    q.push(S);
    p[S]=-1;
    while (!q.empty()){
        int u=q.front();
        used[u]=false;  //不从while循环中直接退出的SPFA的used只要初始化一次就行
        q.pop();
        for (int i=head[u]; i; i=edge[i].next){
            int v=edge[i].v;
            if (edge[i].flow>0 && dis[v]>dis[u]+edge[i].cost){
                dis[v]=dis[u]+edge[i].cost;
                p[v]=i;
                if (!used[v]){
                    used[v]=true;
                    q.push(v);
                }
            }
        }
    }
    if (dis[T]==INF) return false;
    else return true;
}

int MCMF(){
    int max_flow=0;
    int min_cost=0;
    while (SPFA()){
        int flow=INF;
        int u,v;
        for (v=T; p[v]!=-1; v=u){
            u=edge[p[v]].u;
            flow=flow<edge[p[v]].flow ? flow: edge[p[v]].flow;
        }
        for (v=T; p[v]!=-1; v=u){
            u=edge[p[v]].u;
            edge[p[v]].flow-=flow;
            edge[p[v]^1].flow+=flow;
        }
        max_flow+=flow;
        min_cost+=dis[T]*flow;
    }
    if (max_flow==n) return min_cost;
    else             return -1;
}

int main()
{
    while (scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        build_graph();
        printf("%d\n",MCMF());
    }
    return 0;
}

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