Bzoj 3390: [usaco DEC] revenge against the bad cowtractors

Question 3390: [usaco2004 DEC] Time Limit: 1 sec memory limit: 128 MB revenge against bad cowtractors
Submit: 53 solved: 37
[Submit] [Status] Description Niu beiqian was hired to build an Internet between N (2 ≤ n ≤ 1000) sheds. she has explored M (1 ≤ m ≤ 20000) lines that can be built. Each line connects two cowsheds and charges C (1 ≤ C ≤ 100000 ). john, the farmer, is very stingy. He hopes that he will not even pay for the construction at least. bessie decided to retaliate when she learned that the work money was about to blow off. she planned to build some lines to connect all the cowshed together, maximizing John's cost. but she cannot create a ring, so John will find out. 1st rows of input: n, m. rows 2nd to m + 1: Three integers, indicating two endpoints and costs of a possible line. maximum output cost. if a reasonable line cannot be built, output-1 sample input5 8
1 2 3
1 3 7
2 3 10
2 4 4
2 5 8
3 4 6
3 5 2
4 5 17 Sample output42

Connect 4, 5, 2, 5, 2, 3, 1, and 3, and spend 17 + 8 + 10 + 7 = 42 Solutions

This topic is the maximum spanning tree! -1 indicates that a tree cannot be formed.

Code

 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 }

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Bzoj 3390: [usaco DEC] revenge against the bad cowtractors