UVA1658

#include<iostream>
#include<string.h>
#include<vector>
#include<stdio.h>
#include<queue>
using namespace std;
const int INF=0x7fffffff;
const int maxn=2010;
struct Edge
{
int from,to,cap,flow,cost;
Edge(int u,int v,int f,int c,int co):from(u),to(v),flow(f),cap(c),cost(co){};
};
int n,bian,m;
vector<Edge> edges;
vector<int> num[maxn];
int a[maxn],p[maxn],d[maxn];
bool visit[maxn];
void add(int u,int v,int cap,int cost)
{
edges.push_back(Edge(u,v,0,cap,cost));
edges.push_back(Edge(v,u,0,0,-cost));
m+=2;
num[u].push_back(m-2);
num[v].push_back(m-1);
}
void bellman(int s,int t,long long &cost)
{
int i,x;
while(true)
{
for(i=1;i<=(n<<1);i++) d[i]=INF;
memset(visit,0,sizeof(false));
queue<int> q;
q.push(s);
p[s]=0,a[s]=INF,d[s]=0,visit[s]=true;
while(!q.empty())
{
x=q.front(),q.pop(),visit[x]=false;
for(i=0;i<num[x].size();i++)
{
Edge &e=edges[num[x][i]];
if(e.cap>e.flow&&d[e.to]>d[x]+e.cost)
{
a[e.to]=min(a[x],e.cap-e.flow);
p[e.to]=num[x][i];
d[e.to]=d[x]+e.cost;
if(!visit[e.to])
{
visit[e.to]=true;
q.push(e.to);
}
}
}
}
if(d[t]==INF) return ;
for(i=t;i!=s;i=edges[p[i]].from)
{
edges[p[i]].flow+=a[t];
edges[p[i]^1].flow-=a[t];
}
cost+=(long long)d[t]*(long long)a[t];
}
}
int main()
{
int i,from,to,cost;
while(scanf("%d%d",&n,&bian)!=EOF)
{
edges.clear();
for(i=1;i<=(n<<1);i++) num[i].clear();
m=0;
add(1,n+1,2,0);
add(n,n<<1,2,0);
for(i=2;i<n;i++) add(i,i+n,1,0);
for(i=1;i<=bian;i++)
{
scanf("%d%d%d",&from,&to,&cost);
add(from+n,to,1,cost);
}
long long cost=0;
bellman(1,n<<1,cost);
printf("%lld\n",cost);
}
return 0;
}