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>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;

void init(int n, vector<int>& v){
  v.resize(n);
  for(int i = 0; i < n; i++){
    v[i] = i;
  }
}

int root(int a, vector<int>& v){
  if(v[a] == a) return a;
  return (v[a] = root(v[a], v));
}

bool same(int a, int b, vector<int>& v){
  return root(a,v) == root(b,v);
}

void unite(int a, int b, vector<int>& v){
  v[root(a,v)] = root(b,v);
}


int main(){
  int n;
  cin >> n;
  vector<vector<int> > a(n, vector<int>(n, -1));
  for(int i = 0; i < n; i++)
    for(int j = 0; j < n; j++)
      cin >> a[i][j];

  vector<int> cost, src, dst;
  for(int i = 0; i < n; i++){
    for(int j = i+1; j < n; j++){
      if(a[i][j] > -1){
        cost.push_back(a[i][j]);
        src.push_back(i);
        dst.push_back(j);
      }
    }
  }
  vector<pair<int, int> > edges(cost.size());

  for(int i = 0; i < cost.size(); i++)
    edges.push_back(make_pair(cost[i], i));

  sort(edges.begin(),edges.end());

  int sum = 0;
  vector<int> units;
  init(n, units);
  for(int i = 0; i < edges.size(); i++){
    int idx = edges[i].second;
    int s = src[idx], d = dst[idx];
    if(same(s, d, units))
      continue;
    unite(s, d, units);
    sum += cost[idx];
  }

  cout << sum << endl;
}

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<vector>
#include<queue>
#include<algorithm>
using namespace std;

#define INF 20000000
typedef struct Edge edge;

struct Edge{
  int src,dst,weight;
  Edge(int start,int end,int cost) : src(start),dst(end),weight(cost) {}
};

typedef vector<edge> Edges;

bool operator < (const edge &e,const edge &f){
  return (e.weight != f.weight) ? (e.weight > f.weight) : (e.src != f.src) ? (e.src < f.src) : (e.dst < f.dst);
}

class UnionFind{
public:
  int par[1001];
  int rank[1001];

  UnionFind(){
	for(int i = 0;i < 1001;i++){
	  par[i] = i;
	  rank[i] =1;
	}
  }

  int root(int);
  bool findset(int,int);
  void unionset(int,int);
};

void kruskal(Edges);

int main(int argc,char* argv[]){
  int V;
  Edges es;
  int dist;

  cin >> V;
  for(int i = 0;i < V;i++){
	for(int j = 0;j < V;j++){
	  cin >> dist;
	  if(dist != -1){
		edge e(i,j,dist);
		es.push_back(e);
	  }
	}
  }

  kruskal(es);
  return 0;
}

void kruskal(Edges es){
  priority_queue<edge> que;
  int cost = 0;
  UnionFind uf;
  for(int i = 0;i < (int)es.size();i++)
	que.push(es[i]);

  while(!que.empty()){
	edge e = que.top();que.pop();

	if(!uf.findset(e.src,e.dst)){
	  uf.unionset(e.src,e.dst);
	  cost += e.weight;
	}
  }

  printf("%d\n",cost);
}


int UnionFind::root(int x){
  return (par[x] == x) ? x : root(par[x]);
}

bool UnionFind::findset(int x,int y){
  return root(x) == root(y);
}

void UnionFind::unionset(int x,int y){
  x = root(x);
  y = root(y);

  if(x == y)
	return;

  if(rank[y] < rank[x])
	swap(x,y);
  par[y] = x;
  rank[x] += rank[y];
}

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

using namespace std;
const int INF = 1001001001;

int prim(vector< vector<int> > cost)
{
    vector<int> V(1, 0), T(cost.size());
    for(int i=0;i<cost.size();++i) T[i] = i;
    T[0] = INF;
    int mini, minj, min_cost, ans=0;
    while(V.size() < cost.size())
    {
        min_cost = INF;
        for(int i : V){
            for(int j : T)
            {
                if(j == INF) continue;
                if(cost[i][j] < min_cost)
                {
                    mini = i;
                    minj = j;
                    min_cost = cost[i][j];
                }
            }
        }
        V.push_back(minj);
        T[minj] = INF;
        cost[mini][minj] = cost[minj][mini] = INF;
        ans += min_cost;
    }
    return ans;
}

int main()
{
    int n;
    cin >> n;
    vector<vector<int> > cost(n, vector<int>(n));

    for(int i=0;i<n;++i)
    {
        for(int j=0;j<n;++j)
        {
            cin >> cost[i][j];
            if(cost[i][j] == -1) cost[i][j] = INF;
        }
    }

    cout << prim(cost) << endl;
}

C++: #include <stdio.h>

int n,M[110][110];

int minimum(){
  int color[110],d[110],p[110];
  int i=0,s=0;
  int mincost,v,u;
  while(i<=n){color[i]=0;d[i]=5000;p[i]=-1;i++;}
  d[0]=0;
  while(1){
    mincost = 5000;
    for(i=0;i<n;i++){
      if(color[i] != 2 && d[i]<mincost){
	mincost = d[i];
	u=i;
      }
    }
    if(mincost == 5000){
      break;
    }
    color[u] = 2;
    for(v=0;v<n;v++){
      if(color[v] != 2 && M[u][v]<d[v] && M[u][v]!=-1){
	d[v] = M[u][v];
	p[v] = u;
	color[v] = 1;
      }
    }
  }
  for(i=0;i<n;i++){
    if(d[i]!=5000) s+=d[i];
  }
  return s;
}
int main(void){
  int i,j;
  scanf("%d",&n);
  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      scanf("%d",&M[i][j]);
    }
  }
  printf("%d\n",minimum());
  return 0;
}