luogu_1339 [USACO09OCT]热浪Heat Wave

#include <iostream>
#include <cstdio>
#include <queue>
using namespace std;
const int maxn=6210;
const int INF=1<<30;
int n,c,s,t,d[2510];
bool vis[2510];
struct edge{int v,w;};
queue<int> q;
vector<edge> G[maxn];

void spfa(){
	for(int i=1;i<=n;i++)d[i]=INF;
	q.push(s); d[s]=0; vis[s]=1;
	while(!q.empty()){
		int u=q.front(); q.pop(); vis[u]=0;
		for(int i=0;i<G[u].size();i++){
			int v=G[u][i].v,w=G[u][i].w;
			if(d[u]+w<d[v]){
				d[v]=d[u]+w;
				if(!vis[v]){q.push(v); vis[v]=1;}
			}
		}
	}
}

int main(){
	scanf("%d%d%d%d",&n,&c,&s,&t);
	while(c--){
		int u,v,w;
		scanf("%d%d%d",&u,&v,&w);
		G[u].push_back((edge){v,w}); G[v].push_back((edge){u,w}); 
	}
	spfa();
	printf("%d\n",d[t]);
	return 0;
}