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 <cstdlib>
#include <string>
#include <typeinfo>
#include <cstring>
#include <algorithm>
using namespace std;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;
static const int INFTY = (1<<21);
static const int MAX = 100;

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<cstring>
#define MAX 2000200
#define MIN -2000000300
#define INF 1<<30
using namespace std;
int n;
int A[1000][1000];
int d[1000];
bool used[1000];
 
void Init(int n){
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      A[i][j] = INF;
    }
  }
}
 
int prime(){
  for(int i=0;i<n;i++){
    d[i] = INF;
    used[i]=false;
  }
  int ans=0;
  d[0] = 0;
 
  while(true){
    int v = -1;
    for(int i=0;i<n;i++){
      if(!used[i] && (v == -1 || d[v] > d[i]))v = i;
    }
    if(v == -1)break;
    ans+=d[v];
    used[v] = true;   
 
    for(int i=0;i<n;i++){
      d[i] = min(d[i],A[v][i]);
    }
 
  }
  return ans;
}
 
int main(){
  scanf("%d",&n);
  //  Init(n);
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      scanf("%d",&A[i][j]);
      if(A[i][j] == -1)A[i][j] = INF;
    }
  }
  
  printf("%d\n",prime());
  
 
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
#include <queue>
#include <cmath>
using namespace std;
const int maxn=100+10;
const int INF=1<<21;
int n;
int cost[maxn][maxn];
int mincost[maxn];
int vis[maxn];
void prim(int s)
{
    fill(mincost,mincost+n,INF);
    memset(vis,0,sizeof(vis));
    mincost[s]=0;
    int res=0;
    while(true)
    {
        int v=-1;
        for(int u=0; u<n; u++)
        {
            if(!vis[u]&&(v==-1||mincost[u]<mincost[v])) v=u;
        }
        if(v==-1) break;
        vis[v]=1;
        res+=mincost[v];
        for(int i=0; i<n; i++)
        {
            if(cost[v][i]!=-1)   mincost[i]=min(mincost[i],cost[v][i]);
        }

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




}
int main()
{
//    freopen("in.txt","r",stdin);
    scanf("%d",&n);
    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            scanf("%d",&cost[i][j]);
        }
    }
    prim(0);

    return 0;
}

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

int n;
int g[101][101];

int d[101];
char c[101];
int p[101];

void prim() {
    for (int i = 0; i < n; ++i) {
        d[i] = INT_MAX;
        c[i] = 'w';
    }
    c[0] = 'b';
    d[0] = 0;
    while (true) {
        int u, v;
        int mine = INT_MAX;
        for (int j = 0; j < n; ++j) {
            if (c[j] == 'b') {
                u = j;
                for (int k = 0; k < n; ++k) {
                    if(g[u][k] > -1 && g[u][k] <= d[k] && c[k] != 'b' && g[u][k] <= mine) {
                        d[k] = g[u][k];
                        mine = d[k];
                        v = k;
                    }
                }
            }
        }
        p[v] = u;
        c[v] = 'b';
        if(mine == INT_MAX) break;
    }
}

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int w;
            cin >> w;
            g[i][j] = w;
        }
    }
    prim();
    int sum;
    for (int k = 0; k < n; ++k) {
        sum += d[k];
    }
    cout << sum ;


    return 0;
}

C++: #include <bits/stdc++.h>
#include <numeric>
#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define SORT_INV(c) sort((c).begin(), (c).end(), greater<int>())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG true
#define LL long long
#define Num 1000000007
// sort(a.begin(), a.end(), std::greater<int>());
using namespace std;
struct edge
{
    int to, cost;
};

typedef pair<int, int> P;
int main()
{
    int n;
    cin >> n;
    vector<edge> g[n];
    rep(i, n)
    {
        rep(j, n)
        {
            int temp = 0;
            edge ed;
            cin >> temp;
            if (temp == -1)
                ed.cost = INT_MAX;
            else
                ed.cost = temp;
            ed.to = j;
            g[i].push_back(ed);
        }
    }
    //solve by  fast prim
    bool used[n];
    int mincost[n];
    rep(i, n)
    {
        used[i] = false;
        mincost[i] = INT_MAX;
    }
    int ans = 0;
    mincost[0] = 0;
    priority_queue<P, vector<P>, greater<P>> que;
    que.push(P(0, 0));
    while (que.empty() == false)
    {
        auto p = que.top();
        que.pop();
        int v = p.second;
        if (mincost[v] < p.first || used[v] == true)
            continue;
        used[v] = true;
        ans += p.first;
        rep(i, g[v].size())
        {
            auto e = g[v][i];
            mincost[e.to] = min(mincost[e.to], e.cost);
            que.push(P(mincost[e.to], e.to));
        }
    }
    cout<<ans<<endl;
    return 0;
}