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>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cassert>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define rep(i,n) FOR(i,0,n)
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define vint vector<int>
#define vdouble vector<double>
#define vstring vector<string>
using namespace std;

#include<map>
#include<set>
#include<queue>

typedef long long ll;
typedef unsigned long long ull;

const int MAX_N = 1000000;
const int INFTY = (1 << 21); // 2097152
// const ll INFTY = (1 << 60);

class Edge{
public:
	int from, to, cost;
	Edge(int from = 0, int to = 0, int cost = 0) :
			from(from), to(to), cost(cost){}

	bool operator < (const Edge &e) const{
		return cost < e.cost;
	}
	bool operator >(const Edge &e) const{
		return cost > e.cost;
	}

};

class Node{
public:
	vector<Edge> edges;
	int dist;

	Node(){
		dist = INFTY;
	}
};

class Graph{
public:
	vector<Node> nodes;
	Graph(int n) {
		rep(i, n) { Node n;  nodes.push_back(n); }
	}
	Node& operator[](int i){
		return nodes[i];
	}
};

class Data{

public:
	int dist;
	Edge *edge;
	Data(int dist, Edge *edge) {
		this->dist = dist;
		this->edge = edge;
	}

	bool operator < (const Data &d) const{
		return dist < d.dist;
	}
	bool operator >(const Data &d) const{
		return dist > d.dist;
	}
};

Graph G(0);
int N;

int prim(){

    priority_queue<Edge, vector<Edge>, greater<Edge>> pq;
    Edge e0 = Edge(-1, 0, 0);
    pq.push(e0);

    while(!pq.empty()){
        Edge e = pq.top(); pq.pop();
        Node &n = G[e.to];
        if(n.dist != INFTY) continue;
        n.dist = e.cost;
        // cerr << n.dist << endl;

        for(auto &ee: n.edges){
            pq.push(ee);
        }
    }

    int ret = 0;
    rep(i, N) ret += G[i].dist;
    return ret;
}

int main() {
	cin >> N;
	G = Graph(N);

    rep(i, N){
        rep(j, N) {
            int cost;
            cin >> cost;
            if(cost != -1){
                int from = i; int to=j;
                G[from].edges.push_back(Edge(from, to, cost));
            }
        }
    }

	cout << prim() << endl;
}

C++: #include <iostream>
#include <queue>
#include <climits>
using namespace std;

const int N = 100;
int n;
int A[N][N];
bool visit[N] = {0};
priority_queue< pair<int, int> > Q;

int main()
{
	cin >> n;
	for (int i=0; i<n; i++)
	{
		for (int j=0; j<n; j++)
		{
			cin >> A[i][j];
		}
	}

	Q.push(pair<int, int>(0,0));

	int cost = 0;

	while (Q.size())
	{
		pair<int, int> q = Q.top();
		Q.pop();
		int k = q.second;
		if (visit[k]) continue;
		cost += q.first;
		visit[k]=true;
		for(int j=0;j<n;j++)
		{
			int c = A[k][j];
			if (c <= 0) continue;
			if (visit[j]) continue;
			Q.push(pair<int, int>(-c,j));
		}
	}

	cout << -cost << 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, G[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 <bits/stdc++.h>
using namespace std;

#define N_MAX 100

int M[N_MAX][N_MAX];

int main(){

  int n;
  scanf("%d", &n);

  for(int i=0; i<n*n; i++){
    scanf("%d", &M[i/n][i%n]);
  }

  /*
   * Find Mininum Spanning Tree using
   * Prim's Algorithm
  */
  vector<bool> is_belong_to_mst(n, false);
  is_belong_to_mst.at(0) = true;
  int total_cost = 0;
  for(int i=1; i<n; i++){
    // get t and adj
    vector<int> t;
    vector<int> adj;
    for(int i=0; i<n; i++){
      if(is_belong_to_mst.at(i)) t.push_back(i);
      else adj.push_back(i);
    }

    int min_cost = INT_MAX;
    int next_t = 0;
    for(int i=0; i<t.size(); i++){
      for(int j=0; j<adj.size(); j++){
        if(M[t.at(i)][adj.at(j)] != -1 && M[t.at(i)][adj.at(j)] < min_cost){
          min_cost = M[t.at(i)][adj.at(j)];
          next_t = adj.at(j);
        }
      }
    }

    is_belong_to_mst.at(next_t) = true;
    total_cost += min_cost;
  }

  printf("%d\n", total_cost);

  return 0;
}

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

static const int MAX_NUM  = 101;
static const int NO_VISIT  = 0;
static const int NOW_VISIT = 1;
static const int END_VISIT = 2;

void MPT(int *pElem, int num)
{
    int i;
    int mincost;
    int target;
    int parent[MAX_NUM];
    int cost[MAX_NUM];
    int state[MAX_NUM] = {0};
    int *tmp;
    int total = 0;

    for (i = 0; i < num; i++) {
        parent[i] = -1;
        cost[i]   = 0x7FFFFFFF;
    }

    cost[0] = 0;

    for (;;) {
        mincost = 0x7FFFFFFF;
        for (i = 0; i < num; i++) {
            if ((state[i] != END_VISIT) && (mincost > cost[i])) {
                target  = i;
                mincost = cost[i];
            }
        }
        if (mincost == 0x7FFFFFFF) {
            break;
        }

        tmp = pElem + target * MAX_NUM;
        for (i = 0; i < num; i++) {
            if (*(tmp + i) < cost[i]) {
                cost[i]   = *(tmp + i);
                parent[i] = target;
                state[i]  = NOW_VISIT;
            }
        }
        state[target] = END_VISIT;
        total += cost[target];
    }

    printf("%d\n", total);

    return;
}

int main(void)
{
    int i, j;
    int num;
    int tmp;
    int elem[MAX_NUM][MAX_NUM];

    scanf("%d", &num);
    for (i = 0; i < num; i++) {
        for (j = 0; j < num; j++) {
            scanf("%d", &tmp);
            elem[i][j] = (tmp != -1) ? tmp : 0x7FFFFFFF;
        }
    }

    MPT(&elem[0][0], num);

    return 0;
}