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>
using namespace std;
static const int MAX=100;
static const int INFTY=(1<<21);
static const int WHITE=0;
static const int BLACK=1;

int n,M[MAX][MAX];

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

    d[0]=0;
    while(true){
    int minv=INFTY,u=-1;

    for(int i=0;i<n;i++){
        if(color[i]==WHITE&&minv>d[i]){minv=d[i];u=i;}
    }
    if(u==-1)break;
    color[u]=BLACK;
    for(int i=0;i<n;i++){
        if(color[i]==WHITE&&M[u][i]!=INFTY){
            if(d[i]>M[u][i]){
                d[i]=M[u][i];
                p[i]=u;
            }
        }
    }
    }
    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;scanf("%d",&e);
            M[i][j]=(e==-1)?INFTY:e;
        }
    }

    cout<<prim()<<endl;
    return 0;
}

C++: #include <iostream>
using namespace std;

const int WHITE = 0, GRAY = 1, BLACK = 2, INF = 1 << 21;
int n, M[100][100];

int prim()
{
	int u, minv;
	int d[100], p[100], color[100];
	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] != -1){
				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)
		{
			cin >> M[i][j];
		}
	}
	cout << prim() << endl;
	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<iostream>
#define LEN 100
#define NIL -1
using namespace std;

int INFTY = 2000;
int w[LEN][LEN];
int color[LEN];
int n;
int WHITE = 0;
int BLACK = 1;
 
int prim(int x)
{
    int res = 0;
    int cnt = 1;
    color[x] = BLACK;
    while (cnt++ != n) {
        int minCost = INFTY;
        int pos = 0;
        for (int i = 0; i < n; i++) {
            if (color[i] != BLACK) continue;
            for (int j = 0; j < n; j++) {
                if (color[j] != WHITE) continue;
                if (w[i][j] < minCost) {
                    pos = j;
                    minCost = w[i][j];
                }
            }
        }
        res += minCost;
        color[pos] = BLACK;
    }
    return res;
}
 
int main()
{
    cin >> n;
    int num;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> num;
            if (num == NIL) w[i][j] = INFTY;
            else w[i][j] = num;
        }
    }
    cout << prim(0) << endl;
    return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <queue>
#include <utility>

using namespace std;

const int NIL = 2001;
const int MAX = 100;
int G[MAX][MAX];
int color[MAX];
int W[MAX];
int n;

const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;

void MST() {
	priority_queue<pair<int, int>> PQ;
	PQ.push(make_pair(0, 0));
	W[0] = 0;
	color[0] = BLACK;
	while (!PQ.empty()) {
		int u = PQ.top().second;
		PQ.pop();
		color[u] = BLACK;
		for (int i = 0; i < n; ++i) {
			if (G[u][i] != -1 && G[u][i] < W[i] && color[i] != BLACK) {
				PQ.push(make_pair(G[u][i] * -1, i));
				W[i] = G[u][i];
//				cout << u << ":" << i << ":" << G[u][i] << endl;
			}
		}
	}
}

int main() {

	scanf("%d", &n);
	for (int i = 0; i < n; ++i) {
		W[i] = NIL;
		color[i] = WHITE;
	}

	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			int a;
			scanf("%d", &a);
			G[i][j] = a;
		}
	}

	MST();

	int sum = 0;
	for (int i = 0; i < n; ++i) {
//		cout << i << ":" << W[i] << endl;
		sum += W[i];
	}
	cout << sum << endl;

	return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>

using namespace std;

struct edge {
    int from, to, cost;
};
bool asc(const edge& l, const edge& r) {
    return l.cost < r.cost;
}

int main() {
    int n;
    cin >> n;
    vector<edge> E;
    int a;
    for (int i=0; i<n; ++i) {
        for (int j=0; j<n; ++j) {
            cin >> a;
            if (a < 0) continue;
            E.push_back((edge){i, j, a});
        }
    }
    sort(E.begin(), E.end(), asc);

    vector<int> V(1, 0);
    int res = 0;
    while (1) {
        bool update = false;
        for (int i=0; i<(int)E.size(); ++i) {
            bool exist_from = find(V.begin(), V.end(), E[i].from) != V.end();
            bool exist_to = find(V.begin(), V.end(), E[i].to) != V.end();
            if (exist_from && ! exist_to) {
                res += E[i].cost;
                V.push_back(E[i].to);
                update = true;
                break;
            }
        }
        if ( ! update) break;
    }

    cout << res << endl;

    return 0;
}