dijkstra模板

用dijkstra算法时，求最短路，不能存在负权边；求最长路时，不能存在正权边（（（贪心思想；

代码：

struct edge
{
int to,val,next;
}e[maxm];

int vis[maxn],head[maxn],in[maxn];
ll dis[maxn];

int n,m,cnt;

void add(int u,int v,int val)
{
e[cnt] = (edge){v,val,head[u]};
head[u] = cnt++;
}
priority_queue<pii> pq;
void dijkstra(int s)
{
while(!pq.empty())
pq.pop();
pq.push(make_pair(0,s));
for(int i = 0;i<=n+1;i++)
vis[i] = 0;
while(!pq.empty())
{
pii p = pq.top();
int u = p.second;
//cout<<head[u]<<endl;
pq.pop();
if(vis[u])
continue;
vis[u] = 1;
for(int i = head[u];i!=-1;i = e[i].next)
{
//cout<<i<<endl;
int v = e[i].to;
if(!vis[v])
{
if(dis[v]<dis[u]+e[i].val)
{
dis[v] = dis[u]+e[i].val;
// cout<<dis[v]<<endl;
pq.push(make_pair(dis[v],v));
}
}
}
}
}