BZOJ 3390: [Usaco2004 Dec]Bad Cowtractors牛的报复

 1 /*Author:WNJXYK*/
 2 #include<cstdio>
 3 #include<algorithm> 
 4 using namespace std;
 5 const int Maxn=1000;
 6 int father[Maxn+10];
 7 inline void initFather(){
 8     for (int i=1;i<=Maxn;i++) father[i]=i;
 9 }
10 
11 inline int getFather(int x){
12     return father[x]=father[x]==x?x:getFather(father[x]);
13 }
14 
15 inline void mergeFather(int x,int y){
16     int lx=getFather(x),ly=getFather(y);
17     if (lx<ly){
18         father[ly]=lx;
19     }else{
20         father[lx]=ly;
21     }
22 } 
23 
24 struct Edge{
25     int x,y;
26     int w;
27     Edge(){}
28     Edge(int a,int b,int c){
29         x=a;
30         y=b;
31         w=c;
32     }
33 };
34 
35 const int Maxm=20000;
36 Edge e[Maxm+10];
37 
38 bool cmp(Edge a,Edge b){
39     if (a.w>b.w) return true;
40     return false;
41 }
42 
43 int cnt,ans; 
44 
45 int n,m;
46 int main(){
47     scanf("%d%d",&n,&m);
48     initFather();
49     for (int i=1;i<=m;i++){
50         int x,y,z;
51         scanf("%d%d%d",&x,&y,&z);
52         e[i]=Edge(x,y,z);
53     }
54     sort(e+1,e+m+1,cmp);
55     cnt=n;
56     for (int i=1;i<=m;i++){
57         int x=e[i].x,y=e[i].y,w=e[i].w;
58         if (getFather(x)!=getFather(y)){
59             mergeFather(x,y);
60             cnt--;
61             ans+=w;
62         }
63         if (cnt==1) break;
64     }
65     if (cnt!=1){
66         printf("-1\n");
67         return 0;
68     }
69     printf("%d\n",ans);
70     return 0;
71 }