UVALive

 UVALive - 6266 Admiral

题意：找两条完全不相交不重复的路使得权值和最小。

思路：比赛的时候时间都卡在D题了，没有仔细的想这题，其实还是很简单的，将每个点拆开，连一条容量为1，费用为0的边，起点和终点容量为2，两点之间有边就加一条容量为1，费用为权值的边，这样跑一边费用流就可以了。

#pragma comment(linker, "/STACK:1000000000")
#include <bits/stdc++.h>
#define LL long long
#define INF 0x3f3f3f3f
#define IN freopen("in.txt","r",stdin);
#define OUT freopen("out.txt","w",stdout);
using namespace std;
#define MAXN 9999
#define V 2005
#define E 30005
int vis[V];
int dist[V];
int pre[V];

struct Edge{
    int u,v,c,cost,next;
}edge[E];
int head[V],cnt;

void init(){
    cnt=0;
    memset(head,-1,sizeof(head));
}
void addedge(int u,int v,int c,int cost)
{
    edge[cnt].u=u;edge[cnt].v=v;edge[cnt].cost=cost;
    edge[cnt].c=c;edge[cnt].next=head[u];head[u]=cnt++;

    edge[cnt].u=v;edge[cnt].v=u;edge[cnt].cost=-cost;
    edge[cnt].c=0;edge[cnt].next=head[v];head[v]=cnt++;
}

bool spfa(int begin,int end){
    int u,v;
    queue<int> q;
    for(int i=0;i<=end+2;i++){
        pre[i] = -1;
        vis[i] = 0;
        dist[i] = INF;
    }
    vis[begin]=1;
    dist[begin]=0;
    q.push(begin);
    while(!q.empty()){
        u=q.front();
        q.pop();
        vis[u]=0;
        for(int i=head[u];i!=-1;i=edge[i].next){
            if(edge[i].c>0){
                v=edge[i].v;
                if(dist[v]>dist[u]+edge[i].cost){
                    dist[v]=dist[u]+edge[i].cost;
                    pre[v]=i;
                    if(!vis[v]){
                        vis[v]=true;
                        q.push(v);
                    }
                }
            }
        }
    }
    return dist[end] != INF;
}

int MCMF(int begin,int end){
    int ans=0,flow;
    int flow_sum=0;
    while(spfa(begin,end)){
        flow=INF;
        for(int i=pre[end];i!=-1;i=pre[edge[i].u])
            if(edge[i].c<flow)
                flow=edge[i].c;
        for(int i=pre[end];i!=-1;i=pre[edge[i].u]){
            edge[i].c-=flow;
            edge[i^1].c+=flow;
        }
        ans+=dist[end];
        flow_sum += flow;
    }
    //cout << flow_sum << endl;
    return ans;
}

int main()
{
    //IN;
    int n, m, x, y, z;
    while(~scanf("%d%d", &n, &m)){
        init();
        int s = 1, t = 2 * n;
        for(int i = 2; i < n; i++){
            addedge(i, i + n, 1, 0);
        }
        addedge(1, n + 1, 2, 0);
        addedge(n, n << 1, 2, 0);
        for(int i = 1; i <= m; i++){
            scanf("%d%d%d", &x, &y, &z);
            addedge(x + n, y, 1, z);
        }
        int ans = MCMF(s, t);
        printf("%d
", ans);
    }
    return 0;
}