[USACO 102]Agri-Net

OJ题号：POJ1258、洛谷1546

思路：Kruskal。

 #include<cstdio>
 #include<utility>
 #include<vector>
 #include<algorithm>
 #define w first
 #define a second.first
 #define b second.second
 typedef std::pair<int,std::pair<int,int> > Edge;
 const int N=;
 int n;
 std::vector<Edge> e;
 class UnionFindSet {
     private:
         int anc[N];
     public:
         UnionFindSet(int n) {
             for(int i=;i<n;i++) anc[i]=i;
         }
         int Find(int x) {
             return (x==anc[x])?x:(anc[x]=Find(anc[x]));
         }
         void Union(int x,int y) {
             anc[Find(y)]=Find(x);
         }
 };
 int main() {
     scanf("%d",&n);
     for(int i=;i<n;i++) {
         for(int j=;j<n;j++) {
             int c;
             scanf("%d",&c);
             if(i<j) {
                 e.push_back(std::make_pair(c,std::make_pair(i,j)));
             }
         }
     }
     UnionFindSet s(n);
     std::sort(e.begin(),e.end());
     int ans=;
     for(int i=;i<(int)e.size();i++) {
         if(s.Find(e[i].a)==s.Find(e[i].b)) continue;
         ans+=e[i].w;
         s.Union(e[i].a,e[i].b);
     }
     printf("%d\n",ans);
     return ;
 }