POJ 3255

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#define MAX 100005
#define INF 0xfffffff
using namespace std;
typedef struct{
int from, to, next, w;
}Node;
Node edge[2*MAX];
queue<int>q;
int head[MAX], vis[MAX], dist[MAX], rdist[MAX];
void init(int n){
memset(head, -1, sizeof(head));
for(int i = 1;i <= n;i ++)
dist[i] = rdist[i] = INF;
dist[1] = rdist
= 0;
}
void spfa(int s, int dist[]){
while(!q.empty()) q.pop();
memset(vis, 0, sizeof(vis));
q.push(s);
vis[s] = 1;
while(!q.empty()){
int p = q.front();
q.pop();
vis[p] = 0;
for(int i = head[p];i != -1;i = edge[i].next){
int v = edge[i].to;
if(dist[v] > dist[p] + edge[i].w){
dist[v] = dist[p] + edge[i].w;
if(!vis[v]){
q.push(v);
vis[v] = 1;
}
}
}
}
}
void AddEdge(int u, int v, int w, int i){
edge[i].from = u;
edge[i].to = v;
edge[i].w = w;
edge[i].next = head[u];
head[u] = i;
}
int main(){
int R, N, u, v, w, secl;
//freopen("in.c", "r", stdin);
while(~scanf("%d%d", &N, &R)){
init(N);
int i = 0;
for(int j = 0;j < R;j ++){
scanf("%d%d%d", &u, &v, &w);
AddEdge(u, v, w, ++i);
AddEdge(v, u, w, ++i);
}
spfa(1, dist);
spfa(N, rdist);
secl = INF;
for(int j = 1;j <= i;j ++){
u = edge[j].from;
v = edge[j].to;
if(dist[u] + edge[j].w + rdist[v] > dist
&& secl > dist[u] + edge[j].w + rdist[v])
secl = dist[u] + edge[j].w + rdist[v];
}
printf("%d\n", secl);
}
return 0;
}