[原题](http://poj.org/problem?id=3068)
给一个有向带权图,求两条从0-N-1的路径,使它们没有公共点且边权和最小 。
//是不是像传纸条啊~
是否可行只要判断最后最大流是不是2就可以了
#include<cstdio>
#include<queue>
#include<cstring>
#define N 1010*1010
#define inf 0x3f3f3f3f
using namespace std;
int n,m,head[N],dis[N],cur[N],ans,cnt=2,s,t,ANS,T,cse;
queue <int> q;
bool vis[N];
struct hhh
{
int to,next,w,cost;
}edge[1000005];
int read()
{
int ans=0,fu=1;
char j=getchar();
for (;(j<'0' || j>'9') && j!='-';j=getchar()) ;
if (j=='-') fu=-1,j=getchar();
for (;j>='0' && j<='9';j=getchar()) ans*=10,ans+=j-'0';
return ans*fu;
}
void add(int u,int v,int w,int c)
{
edge[cnt].to=v;
edge[cnt].w=w;
edge[cnt].next=head[u];
edge[cnt].cost=c;
head[u]=cnt++;
}
void addEdge(int u,int v,int w,int c)
{
add(u,v,w,c);
add(v,u,0,-c);
}
bool bfs()
{
for (int i=s;i<=t;i++)
vis[i]=0,cur[i]=head[i],dis[i]=inf;
q.push(s);
dis[s]=0;
vis[s]=1;
while(!q.empty())
{
int r=q.front();
q.pop();
vis[r]=0;
for (int i=head[r],v;i;i=edge[i].next)
{
v=edge[i].to;
if (edge[i].w>0 && dis[r]+edge[i].cost<dis[v])
{
dis[v]=dis[r]+edge[i].cost;
if (!vis[v])
{
vis[v]=1;
q.push(v);
}
}
}
}
return dis[t]!=inf;
}
int dfs(int x,int f)
{
if (x==t) return ANS+=f*dis[t],f;
int ha=0,now;
vis[x]=1;
for (int &i=cur[x],v;i;i=edge[i].next)
{
v=edge[i].to;
if (vis[v]) continue;
if (edge[i].w>0 && dis[v]==dis[x]+edge[i].cost)
{
now=dfs(v,min(f-ha,edge[i].w));
if (now)
{
ha+=now;
edge[i].w-=now;
edge[i^1].w+=now;
}
}
if (ha==f) return ha;
}
return ha;
}
void init()
{
memset(head,0,sizeof(head));
cnt=2;
ANS=0;
ans=0;
}
int main()
{
while (~scanf("%d%d",&n,&m))
{
if (!n && !m) break;
++cse;
printf("Instance #%d: ",cse);
s=0;
t=n-1;
init();
for (int i=1,a,b,c;i<=m;i++)
{
a=read();
b=read();
c=read();
addEdge(a,b,1,c);
}
while (bfs()) if (ans==2) break;else ans+=dfs(s,inf);
if (ans==2) printf("%d
",ANS);
else printf("Not possible
");
}
return 0;
}