poj1258 Agri-Net （prim+heap）

题目链接：poj1258 Agri-Net

这题我上个月做过，是个大水题，今天看见有人用prim+heap做的，就学习了下。

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<queue>
 #include<vector>
 #include<set>
 #define CLR(a,b) memset((a),(b),sizeof((a)))
 using namespace std;

 const int inf = 0x3f3f3f3f;
 const int N = ;
 int low[N], s[N];
 int n, ans, num;
 struct Edge{
     int v,c;
     Edge(int _v=,int _c=):v(_v),c(_c){}
     bool operator < (const Edge&r)const{
         return r.c < c;
     }
 };
 vector<Edge>g[N];

 int prim_heap(){
     priority_queue<Edge>q;
     int i, u, v, w;
     Edge p;
     ans = ;//最小生成树总权值
     num = ;//已加入最小生成树的顶点数目
     q.push(Edge(, ));
     while(!q.empty() && num < n){
         p = q.top(); q.pop();
         u = p.v;
         if(s[u]) continue;
         s[u] = ;
         ans += p.c;
         num++;
         for(i = ; i < g[u].size(); ++i){
             v = g[u][i].v;
             if(s[v] == ){
                 w = g[u][i].c;
                 if(w < low[v]){
                     low[v] = w;
                     q.push(Edge(v, w));
                 }
             }
         }
     }
     if(num < n)
         return -;
     return ans;
 }
 int main(){
     int i, j, x;
     while(scanf("%d", &n) == ){
         for(i = ; i < n; ++i)
             g[i].clear();
         for(i = ; i < n; ++i)
             for(j = ; j < n; ++j){
                 scanf("%d", &x);
                 g[i].push_back(Edge(j, x));
         }
         CLR(s, ); CLR(low, inf);
         printf("%d\n",prim_heap());
     }
     return ;
 }