SPFA模板

不能处理有环的图
void SPFA()
{
    memset(vis, false, sizeof(vis));
    vis[1] = true;
    for(int i = 1; i <= n; i++){
        d[i] = cnt[i] = INF;
    }
    d[1] = cnt[1] = 0;
    while(!q.empty()) q.pop();  
    q.push(1);
    while(!q.empty()){
        int u = q.front(); q.pop();
        vis[u] = false;//入队的点开始不能确定是最优的
        for(int i = 0; i < G[u].size(); i++){
            int v = G[u][i].v, w = G[u][i].w;
             if(d[v] > d[u] + w){
                 d[v] = d[u] + w;
                 if(!vis[v]){
                     vis[v] = true;
                     q.push(v);
                }
            }
        }
    }
    printf("%d\n", d[n]);
}