[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=100;
int n;
std::vector<Edge> e;
class UnionFindSet {
    private:
        int anc[N];
    public:
        UnionFindSet(int n) {
            for(int i=0;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=0;i<n;i++) {
        for(int j=0;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=0;
    for(int i=0;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 0;
}