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;

const int MAX = 100;
const int INF = 1 << 29;

int n;
int grid[MAX][MAX];

int prim()
{
	int ans[MAX];
	int visited[MAX];

	for (int i = 0; i < n; i++) {
		ans[i] = INF;
		visited[i] = false;
	}

	ans[0] = 0;

	while (true) {
		int min = INF;
		int min_index;

		for (int i = 0; i < n; i++) {
			if (min > ans[i] && visited[i] == false) {
				min = ans[i];
				min_index = i;
			}
		}

		if (min == INF) {
			break;
		}

		visited[min_index] = true;

		for (int i = 0; i < n; i++) {
			if (ans[i] > grid[min_index][i] && visited[i] == false) {
				ans[i] = grid[min_index][i];
			}
		}
	}

	int sum = 0;

	for (int i = 0; i < n; i++) {
		sum += ans[i];
	}

	return sum;
}

int main()
{
	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int temp;
			cin >> temp;

			if (temp == -1) {
				grid[i][j] = INF;
			}
			else {
				grid[i][j] = temp;
			}
		}
	}

	cout << prim() << endl;

	return 0;
}

C++: #include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>

#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define repi(i,a,b) for(int i = (a); i < (b); i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;

const int INF=1<<29;
const double EPS=1e-9;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
const int MAX_N =200;
int n;
int cost[MAX_N][MAX_N];
bool visit[MAX_N];
int mincost[MAX_N]={INF};
int prime(){
	//memset(mincost, INF, sizeof(mincost));
	memset(visit, false, sizeof(visit));
	int res = 0;
	mincost[0]=0;
	/*rep(i, n){
		cout <<mincost[i];
		cout <<endl;
	}
	cout <<endl;*/
	while(1){
		int v = -1;
		for(int u =0; u <n;u++){
			if(!visit[u]&&(v==-1||mincost[u] < mincost[v])){
				v =u;
			}
		}
		if(v==-1)break;
		//cout <<"v = "<<v<<endl;
		visit[v]=true;
		res +=mincost[v];
		//cout <<res<<endl;
		for(int u =0;u <n ;u++){
			mincost[u]=min(mincost[u],cost[v][u]);
		}
	}
	//cout <<res<<endl;
	return res;
}

int main(){
	cin>>n;
	for(int i =0;i < n;i++){
		mincost[i]=INF;
		for(int j =0;j < n;j++){
			int x;
			cin>>x;
			if(x==-1){
				cost[i][j]=INF;
			}else{
				cost[i][j]=x;
			}
		}
	}
	/*rep(i, n){
		rep(j, n){
			printf("%10d",cost[i][j]);
		}
		cout <<endl;
	}*/

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

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

typedef int Weight;
struct Edge{
	int src,dst;
	Weight weight;
};

bool asc(const Edge &e,const Edge &f){
	return e.weight < f.weight;
}

vector<Edge> Edges;
vector<int> L(100005,-1);

int check(Edge &e,int n){
	int j;
	if (L[e.src]!=L[e.dst]){
		int t = L[e.dst];
		for (j=0;j<n;j++){
			if (L[j]==t){
				L[j]=L[e.src];
			}
		}
		return 1;
	}else{
		return 0;
	}
}

int main(){
	int n,m,i,j,w;
	cin >> n ;
	
	for (i=0;i<n;i++){
		for(j=0;j<n;j++){
			cin >> w;
			if ((w!=-1)&&(i>j)){
				Edge edge={i,j,w};
				Edges.push_back(edge);
			}
		}
	}
	
	sort(Edges.begin(),Edges.end(),asc);
	
	m = Edges.size();
	
	for (j=0;j<n;j++){
		L[j]=j;
	}
	
	int TotalWeight=0;
	int count=0;
	int k;
	for (i=0;i<m;i++){
		if (count==n-1){break;}
		if (check(Edges[i],n)){
			TotalWeight+=Edges[i].weight;
			count++;
		}
	}
	cout << TotalWeight<<endl;
	return 0;
}

C++: #include <stdio.h>

const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
const int N = 100;
const int INF = 2000000000;

int g[N + 1][N + 1];
int d[N + 1], p[N + 1], color[N + 1];
int n;

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

	while (true)
	{
		int min = INF;
		int u = -1;
		for (int i = 1; i <= n; i++)
		{
			if (color[i] != BLACK && d[i] < min)
			{
				min = d[i];
				u = i;
			}
		}
		if (u == -1)
			break;

		color[u] = BLACK;

		for (int i = 1; i <= n; i++)
		{
			if (color[i] != BLACK && g[u][i] != INF && d[i] > g[u][i])
			{
				d[i] = g[u][i];
				color[i] = GRAY;
				p[i] = u;
			}
		}
	}
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		if (p[i] != -1)
			sum += g[p[i]][i];
	}
	printf("%d\n", sum);
}

int main()
{
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= n; j++)
		{
			scanf("%d", &g[i][j]);
			if (g[i][j] == -1)
				g[i][j] = INF;
		}
	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;
}