Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] > 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A > edges[j].A })

	sum := 0
	for len(edges) > 0 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

C++: #include<iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1<<21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, M[MAX][MAX];

int prim(){
   int u, minv;
   int d[MAX], p[MAX], color[MAX];

   for(int i = 0; i < n; i++){
     d[i] = INFTY;
     p[i] = -1;
     color[i] = WHITE;
   }

   d[0] = 0;

   while(1){
     minv = INFTY;
     u = -1;
     for(int i = 0; i < n; i++){
       if(minv > d[i] && color[i] != BLACK){
         u = i;
         minv = d[i];
       }
     }
     if(u == -1) break;
     color[u] = BLACK;
     for(int v = 0; v < n; v++){
       if(color[v] != BLACK && M[u][v] != INFTY){
         if(d[v] > M[u][v]){
           d[v] = M[u][v];
           p[v] = u;
           color[v] = GRAY;
         }
       }
     }
   }
   int sum = 0;
   for(int i = 0; i < n; i++){
     if(p[i] != -1) sum += M[i][p[i]];
   }

   return sum;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      int e; cin >> e;
      M[i][j] = (e == -1) ? INFTY : e;
    }
  }

  cout << prim() << endl;

  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXSIZE = 1e2+7;
const int INF = 1e8+7;
int edge[MAXSIZE][MAXSIZE];
int dis[MAXSIZE];
bool vis[MAXSIZE];
int n;
int prim(){
	memset(vis,false,sizeof(vis));
	for(int i = 1; i <= n; i++){
		dis[i] = edge[1][i];
	}
	vis[1] = true;
	dis[1] = 0;
	int minc, k;
	for(int i = 2; i <= n; i++){
		minc = INF;
		for(int j = 1; j <= n; j++){
			if(!vis[j] && dis[j] < minc){
				minc = dis[j];
				k = j;
			}
		}
		if(minc == INF) break;
		vis[k] = true;
		for(int j = 1; j <= n; j++){
			if(!vis[j] && dis[j] > edge[k][j]){
				dis[j] = edge[k][j];
			}
		}
	}
	int cnt = 0;
	for(int i = 1; i <= n; i++) cnt += dis[i];
	return cnt;
}
int main(){
	while(~scanf("%d",&n)){
		memset(edge,0,sizeof(edge));
		int t;
		for(int i = 1; i <= n; i++){
			for(int j = 1; j <= n; j++){
				scanf("%d",&t);
				if(i == j) continue;
				if(t == -1) edge[i][j] = INF;
				else edge[i][j] = t;
			}
		}
		int res = prim();
		printf("%d\n",res); 
	}
	return 0;
}

C++: #include <bits/stdc++.h>



using namespace std;



static const int INF = 99999;



int main(){



	int n,array[100][100];



	cin>>n;



	for(int i=0; i<n; i++){

		fill(array[i],array[i]+n,INF);

	}



	for(int i=0; i<n; i++){

		for(int j=0; j<n; j++){

			int tmp;

			cin>>tmp;

			if(tmp!=-1) array[i][j]=tmp;

		}

	}



	int ans=INF;

	

	for(int k=0; k<n; k++){

		bool flag[100];

		fill(flag,flag+n,false);

		flag[k]=true;



		int tmp=0;

		while(1){

			int u=-1,minv=INF;

			for(int i=0; i<n; i++){

				if(!flag[i]) continue;

				for(int j=0; j<n; j++){

					if(!flag[j] && array[i][j]<=minv){

						minv = array[i][j];

						u = j;

					}	

				}

			}

			if(minv==INF){

				break;

			}else{

				tmp += minv;

				flag[u]=true;

			}

		}

		ans = min(ans,tmp);

	}



	cout<<ans<<endl;



	return 0;

}

C++: #include <bits/stdc++.h>
using namespace std;
struct edge{
	int v,w;
	edge(){;}
	edge(int v,int w):v(v),w(w){;}
	bool operator<(const edge&p)const{
		return w>p.w;
	}
};
vector<edge> e[105];
priority_queue<edge> q;
bool ok[105];
int main(){
//	freopen("a.txt","r",stdin);
	int n,tem;
	cin>>n;
	for(int i=0;i<n;i++)
		for(int j=0;j<n;j++){
			cin>>tem;
			if(tem!=-1)e[i].push_back(edge(j,tem)),e[j].push_back(edge(i,tem));
		}
	int res=0;
	ok[0]=1;
	int k=0;
	for(int i=0;i<e[0].size();i++)q.push(e[0][i]);
	while(k!=n-1){
		edge te=q.top();q.pop();
		if(ok[te.v])continue;
		else{
			k++;
			ok[te.v]=1;
			res+=te.w;
			for(int i=0;i<e[te.v].size();i++)q.push(e[te.v][i]);
		}
	}
	cout<<res<<endl;
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
struct edge {
    edge() {};
    edge(int s, int e, int d) : start {s}, end {e}, d {d} {};
    bool operator<(edge y){
        return d < y.d || start < y.start || end < y.end;
    };
    bool operator>(edge y){
        return d > y.d || start > y.start || end > y.end;
    };
    bool operator==(edge y){
        return d == y.d || start == y.start || end || y.end;
    };
    int start;
    int end;
    int d;
};

void dfs(vector<vector<int>> graph, bool* used, int id, int n){
    used[id] = true;
    for(int i = 0; i < n; ++i){
        if(graph[id][i] != -1 || used[i]){
            continue;
        }
        dfs(graph, used, i, n);
    }
}

bool is_connected(vector<vector<int>>& graph){
    int n = graph.size();
    bool used[n];
    for(int i = 0; i < n; ++i){
        used[i] = false;
    }
    dfs(graph, used, 0, n);
    for(int i = 0; i < n; ++i){
        if(!used[i]){
            return false;
        }
    }
    return true;
}

void delete_edges(vector<vector<int>>& graph){
    int edges_num = 0;
    vector<edge> vec {};
    int n = graph.size();
    for(int i = 0; i < n; ++i){
        for(int j = i+1; j < n; ++j){
            if(graph[i][j] != -1){
                ++edges_num;
                vec.push_back(edge(i, j, graph[i][j]));
            }
        }
    }
    sort(vec.begin(), vec.end(), [](edge x, edge y){
            return y.d < x.d;
         });

    for(auto it = vec.begin(); it != vec.end(); ++it){
        edge e = *it;
        graph[e.start][e.end] = -1;
        graph[e.end][e.start] = -1;
        if(is_connected(graph)){
            --edges_num;
            if(edges_num == n-1){
                return;
            }
        } else {
            graph[e.start][e.end] = e.d;
            graph[e.end][e.start] = e.d;
        }
    }
}

vector<vector<int>> gen_spanning_tree(vector<vector<int>>& graph){
    vector<vector<int>> tree {graph};
    delete_edges(tree);
    return tree;

}

int calc_weight(vector<vector<int>> graph){
    int sum = 0;
    int n = graph.size();
    for(int i = 0; i < n; ++i){
        for(int j = i+1; j < n; ++j){
            if(graph[i][j] == -1){
                continue;
            }
            sum += graph[i][j];
        }
    }
    return sum;
}

int main(){
    int n;
    cin >> n;
    vector<vector<int>> graph {n, vector<int>(n, 0)};
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j){
            cin >> graph[i][j];
        }
    }
    auto tree = gen_spanning_tree(graph);
    cout << calc_weight(tree) << endl;
}