[USACO09OPEN]捉迷藏Hide and Seek

OJ题号：洛谷2951

思路：Dijkstra+堆优化。注意是无向图，所以加边时要正反各加一遍。

 #include<cstdio>
 #include<vector>
 #include<ext/pb_ds/priority_queue.hpp>
 #define dis first
 #define to second
 const int N=,inf=0x7fffffff;
 typedef std::pair<int,int> Edge;
 int n,m,d[N];
 std::vector<int> e[N];
 void add(int a,int b) {
     e[a].push_back(b);
 }
 void dijkstra() {
     __gnu_pbds::priority_queue<Edge,std::greater<Edge> > q;
     __gnu_pbds::priority_queue<Edge,std::greater<Edge> >::point_iterator a[n+];
     for(int i=;i<=n;i++) {
         a[i]=q.push((i==)?(Edge){,i}:(Edge){inf,i});
         d[i]=(i==)?:inf;
     }
     while(!q.empty()) {
         Edge x=q.top();
         q.pop();
         if(x.dis==inf) continue;
         int u=x.to;
         for(std::vector<int>::iterator i=e[u].begin();i<e[u].end();i++) {
             int& next=*i;
             if(d[u]+<d[next]) {
                 d[next]=d[u]+;
                 q.modify(a[next],(Edge){d[next],next});
             }
         }
     }
 }
 int main() {
     scanf("%d%d",&n,&m);
     for(int i=;i<=m;i++) {
         int a,b;
         scanf("%d%d",&a,&b);
         add(a,b);
         add(b,a);
     }
     dijkstra();
     int id,dis=,count=;
     for(int i=;i<=n;i++) {
         if(d[i]==dis) count++;
         if(d[i]>dis) {
             id=i;
             dis=d[i];
             count=;
         }
     }
     printf("%d %d %d\n",id,dis,count);
     return ;
 }