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
	num := 0
	for len(edges) > 0 && num < n-1 {
		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
		num += 1
	}
	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 <bits/stdc++.h>

#define REP(i, n) for(int i = 0; i < n; i++)
using namespace std;

int P[10010];

void init(int N)
{
    for (int i = 0; i < N; i++) P[i] = i;
}

int root(int a)
{
    if (P[a] == a)  return a;
    return (P[a] = root(P[a]));
}

bool is_same_set(int a, int b)
{
    return root(a) == root(b);
}

void unite(int a, int b)
{
    P[root(a)] = root(b);
}

int main()
{   
    int n;
    cin >> n;

    vector<tuple<int, int, int>> pr;
    int a;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> a;
            if (a != -1 && i <= j) {
                pr.push_back(make_tuple(a, i, j));
            }
        }
    }

    sort(pr.begin(), pr.end());
    init(n);
    int cost = 0;

    for (int i = 0; i < pr.size(); i++) {
        int& a = get<1>(pr[i]);
        int& b = get<2>(pr[i]);

        if (!is_same_set(a, b)) {
            unite(a, b);
            cost += get<0>(pr[i]);
        }
    }
    cout << cost << endl;
}

C++: #include <iostream>

using namespace std;
static const int MAX = 100;
static const int INF = (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] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[0] = 0;

    while (true) {
        minv = INF;
        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] != INF) {
                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 ? INF : e;
        }
    }

    cout << prim() << endl;

    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#define MAX 105
#define INF 1000000
using namespace std;

int n;
int M[MAX][MAX];
int d[MAX];
int p[MAX];
int color[MAX];//0 表示未进入 -1 表示在之中 1 表示已出去

int prim() {
	int u,min,i,j;
	d[0]=0;
	p[0]=-1;
	while(1) {
		min=INF;
		u=-1;
		for(i=0; i<n; i++) {
			if(min>d[i] && color[i]!=1) {
				u=i;
				min=d[i];
			}
		}
		if(u==-1) break;
		color[u]=1;
		for(j=0; j<n; j++) {
			if(color[j]!=1 && M[u][j]!=INF) {
				if(d[j]>M[u][j]) {
					d[j]=M[u][j];
					color[j]=-1;
					p[j]=u;
				}
			}
		}
	}
	int sum=0;
	for(i=0; i<n; i++) {
		if(p[i] != -1) sum+=M[i][p[i]];
	}
	return sum;
}

int main() {
	int i,j,a;
	memset(color,0,sizeof(color));
	memset(d,INF,sizeof(d));
	memset(p,-1,sizeof(p));
	scanf("%d",&n);
	for(i=0; i<n; i++) {
		for(j=0; j<n; j++) {
			scanf("%d",&a);
			if(a==-1) a=INF;
			M[i][j]=a;
		}
	}
	cout<<prim();
	return 0;
}

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 <bits/stdc++.h>
using namespace std;
typedef pair<int,int> P;
typedef pair<int,P> PP;

int par[101], d[101];
priority_queue<PP, vector<PP>, greater<PP> > G;

void init(int n){
	for(int i = 1;i <= n;i++){
		par[i] = i;
		d[i] = 0;
	}
}

int find(int x){
	if(x == par[x])return x;
	return par[x] = find(par[x]);
}

void unite(int x, int y){
	x = find(x);
	y = find(y);
	if(x == y)return ;
	if(d[x] < d[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(d[x] == d[y])d[x]++;
	}
}

bool same(int x, int y){
	return find(x) == find(y);
}

int main(){
	int n, x, y, t;
	scanf("%d", &n);
	init(n);
	
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= n;j++){
			scanf("%d", &t);
			if(t != -1)G.push(PP(t, P(i, j)));
		}
	}
	
	int ans = 0;
	while(!G.empty()){
		PP pp = G.top();G.pop();
		P p = pp.second;
		int cost = pp.first, from = p.first, to = p.second;
		if(same(from, to))continue;
		unite(from, to);
		ans += cost;
	}
	printf("%d\n", ans);
	return 0;
}

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;
	}