Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"math"
	"os"
	"strconv"
	"strings"
)

type color int

const (
	white color = iota // 未訪問
	mst                // MSTとして確定
)

// 頂点
type node struct {
	matrix   []int // 隣接行列
	minToMst int   // MSTへの重み最小値
	parent   int   // 最小値の相手
	color    color
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n := eGetInt(scanner)

	nodes := make([]node, n)
	for i := 0; i < n; i++ {
		nodes[i].matrix = eAtoi((strings.Fields(eGetline(scanner))))
		nodes[i].parent = -1
		nodes[i].minToMst = math.MaxInt16
		nodes[i].color = white
	}

	// 初回はnode[0]がMSTに入るように,minToMstを設定
	nodes[0].minToMst = 0
	for { // 全部チェックするまで

		// どの頂点を新たにMSTに取り込むか
		min := math.MaxInt16
		u := -1
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].minToMst < min {
				u = i
				min = nodes[i].minToMst
			}
		}

		if u == -1 {
			break
		}
		// MSTに追加する頂点決定
		nodes[u].color = mst

		// MSTに属していない頂点それぞれについて,MSTとの最小の重みを更新
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].matrix[u] == -1 {
				// 接してない
				continue
			}
			if nodes[i].matrix[u] < nodes[i].minToMst {
				// node[u]との重みが最小
				nodes[i].minToMst = nodes[i].matrix[u]
				nodes[i].parent = u
			}
		}
	}

	sum := 0
	for _, v := range nodes {
		// node[0]はparentが入っていない
		if v.parent != -1 {
			sum += v.matrix[v.parent]
		}
	}
	fmt.Println(sum)
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include <stdio.h>
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 d[n], p[n];
    int color[n];
    
    for(int i=0; i<n; i++) {
        color[i] = WHITE;
        d[i] = INFTY;
        p[i] = -1;
    }
    
    d[0] = 0;
    
    while(1) {
        int u;
        int mincost = INFTY;
        for (int i=0; i<n; i++) {
            if (color[i] != BLACK && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }
        
        if (mincost == INFTY) break;
        
        color[u] = BLACK;
        
        for (int v=0; v<=n; v++) {
            if (color[v] != BLACK && M[u][v] != INFTY) {
                if(M[u][v] < d[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() {
    scanf("%d", &n);
    for (int i=0; i<n; i++) {
        for (int j=0; j<n; j++) {
            int tmp;
            scanf("%d", &tmp);
            M[i][j] = (tmp == -1) ? INFTY : tmp;
        }
    }
    
    int sum = prim();
    printf("%d\n", sum);
    
    return 0;
}

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

using namespace std;

#define N 101

int main(){

  int n;

  int g[N][N];
  int min=2000;
  int weight[N];
  int sum=0;
  //load n
  cin >>n;

  //load data
  for(int i=1;i<=n;i++){
    for(int j=1;j<=n;j++){
      scanf("%d",&g[i][j]);
    }
  }

  for(int i=1;i<=n;i++){
    for(int j=1;j<=n;j++){
      if(g[i][j]!=-1 &&g[i][j]<min) min=g[i][j];
      weight[i]=min;
    }
  }

  for(int i=1;i<=n;i++){
    sum+=weight[i];
  }

  cout <<sum<<endl;

  return 0;

}

C++: #include <bits/stdc++.h>
#define rep(i,a) for(i=0;i<a;i++)
using namespace std;
static const int W = 0;
static const int G = 1;
static const int B = 2;

void prim(int n, int &total,vector<vector<int> > &M) {
    int i,u,min;
    vector<int> d(n);
    vector<int> p(n);
    vector<int> color(n);

    rep(i,n){
        d[i] = INT_MAX;
        p[i] = -1;
        color[i] = W;
    }
    d[0] = 0;
    while(true){
        min = INT_MAX;
        u = -1;
        rep(i,n){
            if(min > d[i] && color[i] != B) {
                u = i;
                min = d[i];
            }
        }
        if(u==-1) break;
        color[u] = B;
        rep(i,n){
            if(color[i] != B && M[u][i]){
                if(d[i] > M[u][i]) {
                    d[i] = M[u][i];
                    p[i] = u;
                    color[i] = G;
                }
            }
        }
    }
    rep(i,n){
        if(p[i] != -1) total += M[i][p[i]];
    }
}

int main(void) {
    int i,j,n,total = 0;
    vector<vector<int> > M;
    cin >> n;
    M.resize(n);

    rep(i,n){
        M[i].resize(n);
    }
    rep(i,n){
        rep(j,n){
            cin >> M[i][j];
            if(M[i][j] == -1) M[i][j] = INT_MAX;
        }
    }
    prim(n,total,M);
    cout << total << endl;
    return 0;
}

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

int main() {
    int i, j, n, res = 0;
    cin >> n;
    int a[n][n];

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

    vector<int> v;
    set<int> cons;
    v.push_back(0);
    cons.insert(0);
    while (v.size() != n) {
        int nearest_node = 9999;
        int nearest_distance = 9999;
        for (i=0; i<v.size(); i++) {
            for (j=0; j<n; j++) {
                if ((a[i][j] != -1) && (a[i][j] < nearest_distance) && (cons.count(j) == 0)) {
                    nearest_node = j;
                    nearest_distance = a[i][j];
                }
            }
        }
        res += nearest_distance;
        v.push_back(nearest_node);
        cons.insert(nearest_node);
    }
    cout << res << endl;
    return 0;
}