【费用流】 HDU 1853 Cyclic Tour 费用流 完备匹配（裸题）

n个城市m条街道 要求完全匹配

#include <cstdio>#include <cstring>#include <cstdlib>#include <string>#include <iostream>#include <algorithm>#include <sstream>#include <cmath>using namespace std;#include <queue>#include <stack>#include <vector>#include <deque>#include <set>#include <map>#include <time.h>;#define cler(arr, val)    memset(arr, val, sizeof(arr))#define FOR(i,a,b)  for(int i=a;i<=b;i++)#define IN   freopen ("in.txt" , "r" , stdin);#define OUT  freopen ("out.txt" , "w" , stdout);typedef long long  LL;const int MAXN = 500;const int MAXM = 100000;const int INF = 0x3f3f3f3f;//const int INF = 922222;const int mod = 1000000007;struct Edge{    int to,next,cap,flow,cost;} edge[MAXM];int head[MAXN],tol;int pre[MAXN],dis[MAXN];bool vis[MAXN];void init(){    tol=0;    cler(head,-1);}void addedge(int u,int v,int cap,int cost){    edge[tol].to=v;    edge[tol].cap=cap;    edge[tol].cost=cost;    edge[tol].flow=0;    edge[tol].next=head[u];    head[u]=tol++;    edge[tol].to=u;    edge[tol].cap=0;    edge[tol].cost=-cost;    edge[tol].flow=0;    edge[tol].next=head[v];    head[v]=tol++;}bool spfa(int s,int t,int n){    queue<int>q;    for(int i=0; i<n; i++)    {        dis[i]=INF;        vis[i]=false,pre[i]=-1;    }    dis[s]=0;    vis[s]=true;    q.push(s);    while(!q.empty())    {        int u=q.front();        q.pop();        vis[u]=false;        for(int i=head[u]; ~i; i=edge[i].next)        {            int v=edge[i].to;            if(edge[i].cap>edge[i].flow&&dis[v]>dis[u]+edge[i].cost)            {                dis[v]=dis[u]+edge[i].cost;                pre[v]=i;                if(!vis[v])                {                    vis[v]=true;                    q.push(v);                }            }        }    }    if(pre[t]==-1) return false;    else return true;}int mincostmaxflow(int s,int t,int n,int &cost){    int flow=0;    cost=0;    while(spfa(s,t,n))    {        int Min = INF;        for(int i=pre[t]; ~i; i=pre[edge[i^1].to])        {            if(Min>edge[i].cap-edge[i].flow)                Min=edge[i].cap-edge[i].flow;        }        for(int i=pre[t]; ~i; i=pre[edge[i^1].to])        {            edge[i].flow+=Min;            edge[i^1].flow-=Min;            cost+=edge[i].cost*Min;        }        flow+=Min;    }    return flow;}int main(){#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    //freopen("out.txt", "w", stdout);#endif    int n,m;    while(scanf("%d%d",&n,&m)!=EOF)    {        init();        int u,v,d;        for(int i=0; i<m; i++)        {            scanf("%d%d%d",&u,&v,&d);            addedge(u,v+n,1,d);        }        for(int i=1; i<=n; i++)        {            addedge(0,i,1,0);            addedge(i+n,2*n+1,1,0);        }        int cost;        if(mincostmaxflow(0,2*n+1,2*n+2,cost)==n)        printf("%d\n",cost);        else puts("-1");    }    return 0;}