CCF模拟题 最优灌溉

 1 #include <bits/stdc++.h>
 2 #define LL long long
 3 #define INF 0x3f3f3f3f3f3f3f
 4 #define pii pair<int,int>
 5 using namespace std;
 6 const int maxn = 2000;
 7 struct arc{
 8     int to,cost,next;
 9     arc(int x = 0,int y = 0,int z = -1){
10         to = x;
11         cost = y;
12         next = z;
13     }
14 }e[500000];
15 int tot,n,m,head[maxn];
16 LL d[maxn];
17 bool done[maxn];
18 void add(int u,int v,int cost){
19     e[tot] = arc(v,cost,head[u]);
20     head[u] = tot++;
21     e[tot] = arc(u,cost,head[v]);
22     head[v] = tot++;
23 }
24 priority_queue< pii,vector< pii >,greater< pii > >q;
25 LL prim(){
26     while(!q.empty()) q.pop();
27     for(int i = 1; i <= n; ++i){
28         done[i] = false;
29         d[i] = INF;
30     }
31     q.push(make_pair(d[1] = 0,1));
32     LL ans = 0;
33     while(!q.empty()){
34         int u = q.top().second;
35         q.pop();
36         if(done[u]) continue;
37         done[u] = true;
38         ans += d[u];
39         for(int i = head[u]; ~i; i = e[i].next){
40             if(!done[e[i].to] && e[i].cost < d[e[i].to]){
41                 d[e[i].to] = e[i].cost;
42                 q.push(make_pair(d[e[i].to],e[i].to));
43             }
44         }
45     }
46     return ans;
47 }
48 int main(){
49     int u,v,w;
50     while(~scanf("%d %d",&n,&m)){
51         memset(head,-1,sizeof(head));
52         for(int i = tot = 0; i < m; ++i){
53             scanf("%d %d %d",&u,&v,&w);
54             add(u,v,w);
55         }
56         printf("%I64d\n",prim());
57     }
58     return 0;
59 }