//============================================================================
// Name : POJ.cpp
// Author :
// Version :
// Copyright : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <string.h>
#include <stdio.h>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;
/*
* 使用优先队列优化Dijkstra算法
* 复杂度O(ElogE)
* 注意对vector<Edge>E[MAXN]进行初始化后加边
*/
const int INF=0x3f3f3f3f;
const int MAXN=30010;
struct qnode
{
int v;
int c;
qnode(int _v=0,int _c=0):v(_v),c(_c){}
bool operator <(const qnode &r)const
{
return c>r.c;
}
};
struct Edge
{
int v,cost;
int next;
};
Edge edge[200000];
int tol;
int head[MAXN];
bool vis[MAXN];
int dist[MAXN];
void Dijkstra(int n,int start)//点的编号从1开始
{
memset(vis,false,sizeof(vis));
for(int i=1;i<=n;i++)dist[i]=INF;
priority_queue<qnode>que;
while(!que.empty())que.pop();
dist[start]=0;
que.push(qnode(start,0));
qnode tmp;
while(!que.empty())
{
tmp=que.top();
que.pop();
int u=tmp.v;
if(vis[u])continue;
vis[u]=true;
for(int i=head[u];i!=-1;i=edge[i].next)
{
int v=edge[i].v;
int cost=edge[i].cost;
if(!vis[v]&&dist[v]>dist[u]+cost)
{
dist[v]=dist[u]+cost;
que.push(qnode(v,dist[v]));
}
}
}
}
void addedge(int u,int v,int w)
{
edge[tol].v=v;
edge[tol].cost=w;
edge[tol].next=head[u];
head[u]=tol++;
}

int main()
{
// freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
int n,m;
while(scanf("%d%d",&n,&m)==2)
{
tol=0;
memset(head,-1,sizeof(head));
int A,B,C;
while(m--)
{
scanf("%d%d%d",&A,&B,&C);
addedge(A,B,C);
}
Dijkstra(n,1);
printf("%d\n",dist[n]);
}
return 0;
}

数组优化 Dijkstra 最短路