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;
static const int MAX = 100;
static const int INF = (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] = INF;
		p[i] = -1;
		color[i] = WHITE;
	}
	
	d[0] = 0;
	
	while(1){
		minv = INF;
		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] != INF){
				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)?INF:e;
		}
	}
	
	cout << prim() <<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>
#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 << endl;


    return 0;
}

C++: #include <stdio.h>
#include <vector>
#include <queue>
using namespace std;
struct side{
    int n;
    int m;
    int l;
};
side sides[100000];
void mergesort(int l,int r){
    if(l==r)return;
    side temp;
    if(l==r-1){
        if(sides[l].l>sides[r].l){
            temp=sides[l];
            sides[l]=sides[r];
            sides[r]=temp;
        }
        return;
    }
    int mid=(l+r)/2,now=0;
    side b[r-l+1];
    mergesort(l,mid-1);
    mergesort(mid,r);
    for(int i=0;i<=r-l;i++){
        if(sides[i+l-now].l<sides[mid+now].l){
            b[i]=sides[i+l-now];
            if(i+l-now==mid-1){
                for(i++;i<=r-l;i++){
                    b[i]=sides[mid+now];
                    now++;
                }
            }
        }
        else{
            b[i]=sides[mid+now];
            now++;
            if(mid+now>r){
                for(i++;i<=r-l;i++)
                    b[i]=sides[i+l-now];
            }
        }
    }
    for(int i=0;i<=r-l;i++)
        sides[i+l]=b[i];
}
int main(){
    int n,a,ans=0,c=1,now=0;
    bool tree[10000];
    scanf("%d",&n);
    tree[0]=true;
    for(int i=1;i<n;i++){
        tree[i]=false;
    }
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            scanf("%d",&sides[now].l);
            sides[now].n=i;
            sides[now].m=j;
            if(sides[now].l==-1)now--;
            now++;
        }
    }
    mergesort(0,now-1);
    while(c<n){
        a=0;
        while(tree[sides[a].n]==tree[sides[a].m])a++;
        ans+=sides[a].l;
        tree[sides[a].n]=tree[sides[a].m]=true;
        c++;
    }
    printf("%d\n",ans);
}

C++: #include<bits/stdc++.h>
using namespace std;

const int M = 1000000007;

vector<vector<int>> adj;


struct Point {
    int id;
    // double x, y;
    Point() {}
    Point(int id) : id(id) {}
    // Point(double x, double y): x(x), y(y) {}
    int distance(const Point &p) const {
        return adj[id][p.id] == -1 ? M : adj[id][p.id];
    }
};

int calc_mst(const vector<Point>& points) {
    int n = points.size();
    vector<int> dist(n, M);
    vector<bool> visited(n);
    int p = 0;
    int res = 0;
    while (true) {
        visited[p] = true;
        int mind = M, minj = -1;
        for (int j = 0; j < n; ++j) {
            if (visited[j]) continue;
            dist[j] = min(dist[j], points[p].distance(points[j]));
            if (mind > dist[j]) {
                mind = dist[j];
                minj = j;
            }
        }
        if (minj == -1) break;
        p = minj;
        res += mind;
    }
    return res;
}

int main(int argc, char **argv) {
    int n;
    cin >> n;
    adj = vector<vector<int>>(n, vector<int>(n));
    vector<Point> p(n);
    for (int i = 0; i < n; ++i) {
        p[i] = Point(i);
        for (int j = 0; j < n; ++j) {
            cin >> adj[i][j];
        }
    }
    cout << calc_mst(p) << '\n';
    return 0;
}