By yusijia

Updated:

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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
#define MAXN 10000

int n, m, ans;
int father[MAXN];
int ranks[MAXN];

struct Edge{
    int from;
    int to;
    int cost;
}edge[MAXN];

bool cmp(Edge e1, Edge e2)
{
    return e1.cost < e2.cost;
}

void init_set()
{
    for(int i = 0; i < MAXN; i++){
        father[i] = i;
        ranks[i] = 1;
    }
}

int find_set(int x)
{
    return father[x] == x ? father[x] : father[x] = find_set(father[x]);
}

void union_set(int x, int y)
{
    if(ranks[x] >= ranks[y]){
        ranks[x] += ranks[y];    //ranks数组存的是最小生成树已经连通的节点，所以最后只需检查任意一个x的father[x](根)的ranks值就知道是否是最小生成树了
        father[y] = x;
    }
    else{
        ranks[y] += ranks[x];
        father[x] = y;
    }
}

void kruskal()
{
    init_set();
    int allcost = 0;
    sort(edge, edge + ans, cmp);
    for(int i = 0; i < ans; i++){
        int root_x = find_set(edge[i].from);
        int root_y = find_set(edge[i].to);
        if(root_x != root_y){
            union_set(root_x, root_y);
            allcost += edge[i].cost;
        }
    }
    printf("%d\n", allcost);
}

int main()
{
    freopen("input.txt", "r", stdin);
    int a;
    while(scanf("%d", &n) != EOF){
        ans = 0;
        for(int i = 1; i <= n; i++){
            for(int j = 1; j <= n; j++){
                scanf("%d", &a);
                if(j > i){//这里只存了一半的图
                    edge[ans].from = i;   //注意这里是edge[ans],ans存边数
                    edge[ans].to = j;
                    edge[ans++].cost = a;
                }
            }
        }
        kruskal();
    }
    return 0;
}
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