luogu P1546 最短网络 Agri-Net

#include<cstdio>
#include<algorithm>
using namespace std;
#define maxn 20010

int fa[maxn],n;
int cnt,ans;

struct EDGE {
    int to,from,weight;
} edge[maxn];

void add(int x,int y,int w) {
    edge[++cnt].to = y;
    edge[cnt].from = x;
    edge[cnt].weight = w;
}

int get(int x) {
    if(fa[x] == x)
        return x;
    return fa[x] = get(fa[x]);
}

int cmp(EDGE x,EDGE y) {
    return x.weight < y.weight;
}

int kruskal() {
    for(int i = 1; i <= n; i++)
        fa[i] = i;
    sort(edge + 1,edge + cnt + 1,cmp);
    for(int i = 1; i <= cnt; i++) {
        int l = get(edge[i].from);
        int r = get(edge[i].to);
        if(l != r) {
            fa[l] = r;
            ans += edge[i].weight;
        }
    }
    return ans;
}

int main() {
    scanf("%d",&n);
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= n; j++) {
            int w;
            scanf("%d",&w);
            if(j > i)
            add(i,j,w);
        }
    printf("%d",kruskal());
    return 0;
}