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 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;
int map[101][101];
int dp[101];
bool decided[101];
int sum,n;
int node,nextnode,mincost;
void check(){
	node=1;
	decided[node]=true;
	dp[node]=0;
	while(1){
		nextnode=-1;
		mincost=20000;
		dp[node]=0;
		for(int i=1;i<=n;i++){
			if(map[node][i]==-1||decided[i])continue;

			if(dp[i]==-1){
				dp[i]=map[node][i]+dp[node];
			}else{
				dp[i]=min(dp[i],map[node][i]+dp[node]);
			}
			if(mincost>dp[i])nextnode=i;
		}
		if(nextnode==-1)break;
		sum+=map[node][nextnode];
		decided[nextnode]=true;
		node=nextnode;
	}
}

int main(){
	cin >>n;
	for(int i=1;i<=n;i++){
		dp[i]=-1;
	}

	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin >> map[i][j];
		}
	}

	check();
	cout << sum<<endl;
}

C++: #include<iostream>
#define MAX 100
#define INF (2<<29)
using namespace std;
int main(){
  int n;
  cin>>n;
  int graph[MAX][MAX];
  
  for(int i=1;i<n+1;i++){
    for(int j=1;j<n+1;j++){
      cin>>graph[i][j];
      if(graph[i][j]==-1)graph[i][j]=INF;
    }
  }
  
  int visited[MAX];
  int min[MAX];
  for(int i=1;i<n+1;i++){
    visited[i]=0;
    min[i]=INF;
  }
  
  min[1]=0;
  int ans=0;
  while(true){
    int a=-1;
    for(int i=1;i<n+1;i++){
      if(visited[i]==0&&(a==-1||min[i]<min[a]))a=i;
    }

    if(a==-1)break;
    visited[a]=1;
    ans +=min[a];

    for(int i=1;i<n+1;i++){
      min[i]=min[i]<graph[a][i] ? min[i]:graph[a][i];
    }
  }
  cout<<ans<<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<bits/stdc++.h>
#define REP(i,n) for(int i=0;i<n;i++)
#define LOOP(i,x,n) for(int i=x;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define MP make_pair
#define FIR first
#define SEC second
#define int long long
using namespace std;
const int MOD=1000000007;
const int INF=1000000009;

typedef int Weight;
struct Edge{
  int src;int dst;
  Weight wei;
  Edge(int s=0,int d=0,Weight w=0):
    src(s),dst(d),wei(w){}
};
using Graph = vector<vector<Edge>>;
int prim(const Graph &g,const int r=0){
  struct comp{
    bool operator()(const Edge &e,const Edge &f)const {return e.wei>f.wei;}
  };
  Weight sum=0;
  vector<int> used(g.size());
  priority_queue<Edge,vector<Edge>,comp> q;
  q.emplace(-1,r,0);
  while(q.size()){
    Edge e=q.top();
    q.pop();
    if(used[e.dst])continue;
    used[e.dst]=1;
    sum+=e.wei;
    for(auto &f : g[e.dst]){
      if(!used[f.dst])q.emplace(f);
    }
  }
  return sum;
}

signed main(){
  int n;
  cin>>n;
  Graph g(n);
  REP(i,n)REP(j,n){
    int a;
    cin>>a;
    if(a!=-1){
      g[i].emplace_back(i,j,a);
    }
  }
  cout<<prim(g,0)<<endl;
  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
#define ll long long
#define inf  999999999
#define pa pair<int,int>

using namespace std;

int n,a[200][200]={0};
void prim(){
	int d[200]={0};
	priority_queue<pair<int,pa> >  PQ; 
	pair<int,pa> q;
	pa r;
	int wei=0;
	int w=6;
	int u=w,z=0;
	d[w]=1;
	while(z!=n-1){
		for(int j=n-1;j>-1;j--){
			if(a[u][j]<=0 && d[j]==0 && u!=j) PQ.push(make_pair(a[u][j],make_pair(u,j)));
		}
	while(1){
		if(PQ.size()==0) {
			cout<<"dv"<<endl;
		break;
		}
		q=PQ.top();
		PQ.pop();
		r=q.second;
	//	cout<<"rsec"<<r.second<<endl;
		if(d[r.second]==0) break;
		
		}
	u=r.second;
//	cout<<"a" <<u<<endl;
	d[u]=1;
	wei=wei+q.first;
	z++;
//	cout<<z<<" "<<-q.first<<" "<<u<<" "<<r.first<<endl;
	
	}
	cout<<-wei<<endl;
}



int main(){
	// your code goes here
	int m;
	cin>>n;
	
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
		cin>>m;
		a[i][j]=-m;
		}
	}
	prim();

	return 0;
}

C++: #include<iostream>
using namespace std;
const int MAX = 100;
const int INF = 20000;
int n, G[MAX][MAX], dis[MAX];
bool book[MAX] = { false };
int main()
{
	cin >> n;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> G[i][j];
	for (int i = 0; i < n; i++)
		dis[i] = G[0][i];
	book[0] = true;
	int sum = 0;
	for (int k = 1; k <= n - 1; k++)
	{
		int min = INF;
		int u;
		for (int j = 0; j < n; j++)
			if (!book[j] && dis[j] != -1 && dis[j] < min)
			{
				min = dis[j];
				u = j;
			}
		book[u] = true;
		sum += dis[u];
		for (int v = 0; v < n; v++)
			if (!book[v] && G[u][v] != -1)
				if (dis[v] == -1)
					dis[v] = G[u][v];
				else
					if (dis[v] > G[u][v])
						dis[v] = G[u][v];
	}
	cout << sum << endl;
}