SPFA

queue<int> q;
while(!q.empty())
{
int now=q.front();
q.pop();
for(int e=head[now];e!=-1;e=map[e].next)
{
if(dis[map[e].y]==-1)//没进过队
{
/*1*/q.push(map[e].y);
/*2*/dis[map[e].y]=dis[now]+1;
}
}
}

while(!e.empty())
{
int now=q.front(),q.pop();
for()//省略
{
flag[now]=0;
if(dis[now]+map[e].w<dis[map[e.y]])
{
dis[map[e].y]=map[e].w+dis[now];
if(flag[map[e].y]==0)
{
q.push(map[e].y);
flag[map[e].y]=1;
}
}
}
}