Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

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 prim(int n, int m[MAX][MAX]) {
    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 (true) {
        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() {
    int n, m[MAX][MAX];
    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(n, m) << endl;
}

C++: #include <iostream>
#include <string>
#include <unordered_map>
#include <stdio.h>
#include <list>
#include <vector>
#include <algorithm>
#include <stack>
#include <climits>
#include <queue>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; ++i)
typedef long long ll;

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

	int M[100][100];
	int d[100], p[100];
	int color[100];
	
	rep(i,n)
	{
		rep(j,n)
		{
			cin >> M[i][j];
		}
	}

	rep(i,n)
	{
		color[i]=0;
		d[i]  = INT_MAX;
	}


	d[0] = 0;
	p[0] = -1;

	while(1)
	{
		
		int u;
		int mincost = INT_MAX;
		rep(i,n)
		{
			if(color[i]!=2&&d[i]<mincost)
			{
				mincost = d[i];
				u = i;
			}
		}

		if(mincost==INT_MAX)break;
		//cout<<mincost<<endl;
		color[u] = 2;

		rep(v,n)
		{
			if(color[v] != 2 && M[u][v]!= -1)
			{
				if(M[u][v] < d[v])
				{
					//cout<<M[u][v]<<endl;
					
					d[v] = M[u][v];
					p[v] = u;
					color[v]=1;
				}
			}
		}
	}
	int sum = 0;
	rep(i,n)
	sum+= d[i];
	cout<<sum<<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>
#include <vector>
#include <utility>

using namespace std;

int P[10001];

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);
}

bool span(int n) {
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			if (!is_same_set(i, j))
				return false;
		}
	}
	return true;
}

int main() {
	int n;
	cin >> n;
	init(n);
	vector<vector<int> > map(n, vector<int>(n));
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> map[i][j];
		}
	}
	vector<pair<int, pair<int, int> > > edges;
	for (int i = 0; i < n; i++) {
		for (int j = i; j < n; j++) {
			if (map[i][j] >= 0)
				edges.push_back(pair<int, pair<int, int> >(map[i][j], pair<int, int>(i, j)));
		}
	}
	sort(edges.begin(), edges.end());
	int result = 0;
	while (!span(n)) {
		pair<int, pair<int, int> > edge = edges.front();
		edges.erase(edges.begin());
		int a = edge.second.first;
		int b = edge.second.second;
		if (!is_same_set(a, b)){
			unite(a, b);
			result += edge.first;
		}
	}
	cout << result << endl;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
const int MAXN = 100 + 4;
const int INF = 0x3f3f3f3f;
const int WHITE = 0;
const int BLACK = 1;
const int GRAY = 2;
int G[MAXN][MAXN];
int d[MAXN], p[MAXN], status[MAXN];
int N;

int prim()
{
    int u, min_d;
    memset ( p, -1, sizeof(p) );
    memset ( status, WHITE , sizeof(status) );
    d[0] = 0;
    for ( int i = 1; i <= N; i++ ) d[i] = INF;

    while ( true ) {
        min_d = INF;
        u = -1;
        for ( int i = 0; i < N; i++ ) {
            if ( min_d > d[i] && status[i] != BLACK ) {
                u = i;
                min_d = d[i];
            }
        }

        if ( u == -1 ) break;
        status[u] = BLACK;
        for ( int v = 0; v < N; v++ ) {
            if ( G[u][v] != INF && status[v] != BLACK ) {
                if ( d[v] > G[u][v] ) {
                    d[v] = G[u][v];
                    p[v] = u;
                    status[v] = GRAY;
                }
            }
        }
    }
    int sum = 0;
    for ( int i = 0; i < N; i++ )
        if ( p[i] != -1 ) sum += G[i][p[i]];

    return sum;
}

int main()
{
    int e;
    cin>>N;
    for ( int i = 0; i < N; i++ ) {
        for ( int j = 0; j < N; j++ ) {
            cin>>e;
            G[i][j] = e == -1 ? INF : e;
        }
    }
    int ans = prim();
    cout<<ans<<endl;
}