Go: package main

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

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

C++: #include <iostream>

using namespace std;

static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;
static const int LEN=100;
static const int INF=(1<<21);

int n,M[LEN][LEN];


int prim()
{
    int u,minc;
    int d[LEN],node[LEN],color[LEN];
    for(int i=0; i<n; i++){
        node[i]=-1;
        d[i]=INF;
        color[i]=WHITE;
    }
    d[0]=0;

    while(1){
        minc=INF;
        u=-1;
        for(int i=0;i<n;i++){
            if(d[i]<minc && color[i]!=BLACK){
                u=i; minc=d[i];
            }
        }

        if(u==-1) break;
        color[u]= BLACK;

        for(int i=0;i<n;i++){
            if(color[i]!=BLACK && M[u][i]!=INF){
                if(M[u][i]<d[i]){
                    d[i]=M[u][i];
                    node[i]=u;
                    color[i]=GRAY;
                }
            }
        }
    }
    int sum=0;
    for(int i=0;i<n;i++){
        if(node[i]!=-1) sum+=M[i][node[i]];
    }
    return sum;
}



int main()
{
    cin>>n;
    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            int k;
            cin>>k;
            M[i][j]=(k==-1?INF:k);
        }
    }
    cout<<prim()<<endl;

    return 0;
}

C++: #include<cstdio>
#include<stdlib.h>
#include<iostream>

using namespace std;

const int maxn = 105;

int M[maxn][maxn];
int visit[maxn];
int d[maxn];
int p[maxn];
int n;


int main(){
	cin >> n;
	for(int i = 0;i < n;i++){
		visit[i] = false;
		d[i] = 0x3f3f3f;
		for(int j = 0;j < n;j++){
			cin >> M[i][j];
		}
	}
	int result = 0;
	d[0] = 0;
	while(true){
		int min_distance = 0x3f3f3f;
		int u;
		for(int j = 0;j < n;j++){ 
			if(d[j] < min_distance && (!visit[j])){
				min_distance = d[j];
				u = j;
			}
		}
//		cout << u << endl;
		if(min_distance == 0x3f3f3f)break;
		result += min_distance;
		visit[u] = true;
		d[u] = min_distance;
		for(int s = 0;s < n;s++){
			if(M[u][s] == -1)continue;
			if(M[u][s] < d[s]){
				d[s] = M[u][s];
				p[s] = u;
			}
		}
//		for(int s = 0;s < n;s++)cout << d[s] <<" ";
//		cout << endl;
	}
	cout << result << endl;
	
	
}

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


using namespace std;

int P[110];

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);
}

int main(){
    int n; 
    cin >> n; 
    int w;
    init(n);
    vector< pair<int, pair<int, int> > > edges;
    for (int i = 0; i < n; i++){
        for (int j = i; j < n; j++){
            cin >> w;
            if (w != -1) edges.push_back(make_pair(w, make_pair(i, j)));
        }
    }
    sort(edges.begin(),edges.end());
    int sum = 0;
    while(!edges.empty()){
        pair<int, pair<int, int> > edge = edges[0];
        edges.erase(edges.begin());
        int cost = edge.first;
        int src = edge.second.first;
        int dst = edge.second.second;
        cout << cost << " " << src << " " << dst << endl;
        if (!is_same_set(src, dst)){
            cout << "unite " << src << " " <<  dst << " cost = " << cost << endl;
            unite(src, dst);
            sum += cost;
        }
    }
    cout << sum << endl;
}

C++: #include <iostream>
#include <climits>
#include <queue>

using namespace std;
static const int MAX=100;
static const int WHITE=1;
static const int GRAY=2;
static const int BLACK=3;

int n,M[MAX+10][MAX+10];

int prim()
{
    int u,minv;
    int d[MAX],p[MAX],color[MAX];

    for(int i=0;i<n;i++)
    {
      d[i]=INT_MAX;
      p[i]=-1;
      color[i]=BLACK;
    }

    d[0]=0;

    while(1)
    {
        minv=INT_MAX;
        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]!=INT_MAX)
        {
            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)? INT_MAX:e;
    }

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

C++: #include<bits/stdc++.h>
#define ll long long int
#define FOR(i,a,b) for(ll i=(ll)(a);i<(ll)(b);i++)
#define REP(i,n) FOR(i,0,n)
#define REP1(i,n) FOR(i,1,n)
 
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];

  REP(i, n) {
    d[i] = INFTY;
    p[i] = -1;
    color[i] = white;
  }

  d[0] = 0;

  while( 1 ) {
    minv = INFTY;
    u = -1;
    REP(i, n) {
      if (minv > d[i] && color[i] != black ) {
        u = i;
        minv = d[i];
      }
    }
    if (u == -1) break;
    color[u] = black;
    REP(v, n) {
      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;
  REP(i, n) {
    if (p[i] != -1) sum += M[i][p[i]];
  }
  return sum;
}

int main() {
  cin >> n;
  REP(i, n) {
    REP(j, n) {
      int e;
      cin >> e;
      M[i][j] = (e == -1) ? INFTY : e;
    }
  }
  cout << prim() << endl;
  return 0;
}