Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX   = 100
	INFTY = (1 << 21)
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

//V: グラフの頂点全体の集合
//T: MSTに属する頂点の集合
var (
	n     int
	M     [MAX][MAX]int //重みを記録する隣接行列
	color [MAX]int
	p     [MAX]int //MSTにおける頂点の親を記録
	d     [MAX]int //Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを記録
)

func prim() int {
	var u, minv int
	//初期化
	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}

	d[0] = 0

	for {
		//頂点uを決めていく
		//つまり、Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを決める
		minv = INFTY
		u = -1
		for i := 0; i < n; i++ {
			//未訪問かつ、辺の重みが最小となるuを選ぶ
			if minv > d[i] && color[i] != BLACK {
				u = i
				minv = d[i]
			}
		}

		if u == -1 {
			break
		}

		color[u] = BLACK
		for v := 0; v < n; v++ {
			//未訪問かつ、辺が存在するとき
			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
				}
			}
		}
	}

	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {

		for j := 0; j < n; j++ {
			tmp := nextInt()
			if tmp == -1 {
				tmp = INFTY
			}
			M[i][j] = tmp
		}

	}

	fmt.Println(prim())

}

C++: #include <iostream>
using namespace std;
#define MAX 100
#define INFTY (1<<21)
#define WHITE 0
#define GRAY 1
#define 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;
            if(e==-1) {
                M[i][j] = INFTY;
            }
            else {
                M[i][j] = e;
            }
        }
    }

    cout << prim() << endl;

    return 0;
}

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

using namespace std;

struct Edge{
  int cost, x, y;
};

bool operator < (Edge a, Edge b) {
  return a.cost < b.cost;
}

vector<int> UFtree;

int root(int i) {
  if(UFtree[i] == i) return i;
  return (UFtree[i] = root(UFtree[i]));
}

bool is_same_set(int i, int j) {
  return root(i) == root(j);
}

void unite(int i, int j) {
  UFtree[root(i)] = root(j);
}

int main() {
  int n, cost, w = 0;
  cin >> n;
  for(int i = 0; i < n; i++) UFtree.push_back(i);
  vector<Edge> Edges;
  Edge e;
  for(int i = 0; i < n; i++) {
    for(int j = 0; j < n; j++) {
	cin >> cost;
	if(j > i && cost != -1) {
	  e.cost = cost; e.x = i; e.y = j;
	  Edges.push_back(e);
	}
    }
  }
  sort(Edges.begin(), Edges.end());
  for(int i = 0; i < Edges.size(); i++) {
    if(!is_same_set(Edges[i].x, Edges[i].y)) {
      w += Edges[i].cost;
      unite(Edges[i].x, Edges[i].y);
    }
  }
  cout << w << endl;
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>
using namespace std;
typedef vector <int> vi;
typedef vector <vi> vvi;

class blanch{
	public:
		int weight;
		int from;
		int to;
		blanch():
			weight(0),from(0),to(0){};
		blanch(int newweight, int newfrom, int newto):
			weight(newweight),from(newfrom),to(newto){};
};
typedef vector <blanch> vb;

bool operator<( const blanch &blanch1, const blanch &blanch2){
	return (blanch1.weight > blanch2.weight);
	}

bool operator>( const blanch &blanch1, const blanch &blanch2){
	return (blanch1.weight < blanch2.weight);
	}

int make_graph(vvi &graph, vi &stamp){
	int n=graph.size();
	for (int j=0; j<n; j++){
		for (int i=0; i<n; i++){
			cin>>graph[i][j];
		}
		stamp[j] = 0;
	}
	return 0;
}

int Minimum_Spanning_Tree(vvi &graph, vi &stamp){

	priority_queue<blanch, vb, less<vb::value_type> > pq;
	int n = graph.size(), p1=0, total=0;
	stamp[p1] = 1;

	while (p1!=-1){
		for (int p2=0; p2<n; p2++){
			int *tmp = &graph[p1][p2];
			if (*tmp!=-1 && stamp[p2]==0){
				pq.push(blanch(*tmp, p1, p2));
			}
		}
		p1 = -1;
		while (! pq.empty()){
			blanch tmp = pq.top();
			if (stamp[tmp.from]==1 && stamp[tmp.to]==0){
				p1 = tmp.to;
				stamp[p1] = 1;
				total += tmp.weight;
				pq.pop();
				break;
			}
			pq.pop();
		}
	}
	return total;
}

int main(void){

	int n;
	cin>>n;
	vvi G(n, vi(n));
	vi stamp(n);

	make_graph(G, stamp);

	cout<<Minimum_Spanning_Tree(G, stamp)<<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>
using namespace std;
#define MAX 100
#define INF 1 << 30
int n, A[MAX + 1][MAX + 1], d[MAX + 1];
bool vis[MAX + 1];

int prim(int s){
  int sum = 0;
  for ( int i = 1; i <= n; i++){
    d[i] = A[s][i];
    vis[i] = false;
  }
  d[s] = 0;
  vis[s] = true;

  while ( 1 ){
    int minCost = INF;
    for ( int i = 1; i<=n; i++){
      if ( minCost > d[i] && !vis[i]){
        minCost = d[i];
        s = i;
      }
    }

    if ( minCost == INF)break;

    sum += minCost;
    vis[s] = true;

    for ( int i = 1; i <= n; i++){
      if ( d[i] > A[s][i] && !vis[i]){
        d[i] = A[s][i];
      }
    }
  }

  return sum;
}

int main(){
  cin >> n;
  int a;
  for ( int i = 1; i <= n; i++){
    for ( int j = 1; j <= n; j++){
      cin >> a;
      A[i][j] = ( a == -1 ) ? INF : a;
    }
  }

  cout << prim(1) << endl;

  return 0;
}