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 <iostream>
using namespace std;

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INFTY 1000000


int n,M[100][100],color[100],d[100],p[100];


int prim(){
  int i,u;
  
  for( i = 0; i < 100; i++ ){ 
    color[i] = WHITE;
    d[i] = INFTY;
    p[i] = -1;   
  }

  d[0] = 0;
 
  while(1){
    u = -1;
    int mincost = INFTY;
    
    for( i = 0; i < n; i++ ){
      if( color[i] != BLACK && d[i] < mincost ){
	mincost = d[i];
	u = i;
      }
    }
    
    if( u == -1 ) 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( i = 0; i < n; i++ ){
    if( p[i] != -1 ) sum+= M[i][p[i]];
  }
  return sum;
}

int main(){
  int i,j;
  //,n;
    
  cin >> n;
  for( i = 0; i < n; i++ ){
    for( j = 0; j < n; j++ ){
      cin >> M[i][j];
      if( M[i][j] == -1 ) M[i][j] = INFTY;
    }
  }

  cout << prim() << endl;

  return 0;
}

C++: #include <iostream>
#include <map>
#include <vector>
using namespace std;
typedef vector <int> vi;
typedef vector <vi> vvi;
struct edge{
	int from;
	int to;
};
typedef multimap <int, edge, less<int> > mme;

int addedge(vvi &graph, int y, int x, int val=1){
	graph[y][x] = val;
	return val;
}

int make_graph(vvi &graph, vi &stamp){
	int n=graph.size(), val;

	for (int j=0; j<n; j++){
		for (int i=0; i<n; i++){
			cin>>val;
			addedge(graph, i, j, val);
		}
		stamp[j] = 0;
	}
	return 0;
}

int Minimum_Spanning_Tree(vvi &graph, vi &stamp){

	mme edges;
	int n = graph.size(), p1, p2, p3, total=0;
	p1=0;
	stamp[p1] = 1;

	while (p1!=-1){
		for (int p2=0; p2<n; p2++){
			int *tmp=&graph[p1][p2];
			if (*tmp!=-1 && stamp[p2]==0){
				edge e;
				e.from = p1;
				e.to = p2;
				edges.insert(pair <int, edge> (*tmp, e));
			}
		}
		p1=-1;
		while (! edges.empty()){
			auto it = edges.begin();
			if (stamp[it->second.from]==1 && stamp[it->second.to]==0){
				p1 = it->second.to;
				stamp[p1]=1;
				total+=it->first;
				edges.erase(it);
				break;
			}
			edges.erase(it);
		}
	}
	return total;
}

int resultout(vvi &graph){
	for (int i=0; i<int(graph.size()); i++){
		for (int j=0; j<int(graph.size()); j++){
		cout<<graph[i][j]<<" ";
		}
		cout<<endl;
	}
	return 0;
}

int main(void){

	int n, row;
	cin>>n;
	vvi G(n, vi(n));
	vi stamp(n);

	make_graph(G, stamp);

	cout<<Minimum_Spanning_Tree(G, stamp)<<endl;

	return 0;
}

C++: #include<iostream>
#include<cstdio>
#define W 0
#define G 1
#define B 2
#define inf 5000
#define MAX 100
#define NIL -1
using namespace std;

int n;
int A[MAX][MAX];

int Prim(){
    int color[MAX],d[MAX],p[MAX];
    int min,u,sum = 0;
    for(int i = 0; i < n; i++){
        color[i] = W;
        d[i] = inf;
        p[i] = NIL;
    }
    
    d[0] = 0;
    
    while(1){
        u = -1;
        min = inf;
        for(int i = 0; i < n; i++){
            if(d[i] < min && color[i] != B){
                u = i;
                min = d[i];
            }
        }
        
        if(u == -1) break;
            
        color[u] = B;
            
        for(int i = 0; i < n; i++){
            if(color[i] != B && A[u][i] != NIL){
                if(A[u][i] < d[i]){
                    d[i] = A[u][i];
                    color[i] = G;
                    p[i] = u;
                }
            }
        }
    }
    
    for(int i = 0; i < n; i++) {
        
        if(p[i] != -1) sum += A[i][p[i]];
        
    }
    
    return sum;
     
}

int main(){
    int x;
    scanf("%d",&n);
    for(int i = 0; i < n; i ++){
        for(int j = 0; j < n; j++){
            scanf("%d",&x);
            if( x == -1) A[i][j] = NIL;
            else A[i][j] = x; 
        }
    }
    
    cout << Prim() << endl;
    return 0;
}

C++: #if 0
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??¢?????????????????§??????????????¢??°????????£????????????sum????¨??????¨????????????????????£????????§?????????
???????????¢??????????????§????????????????????????????????????"-1"???????????????????????????????????§???????????§????????¨???????°???????????????????
#endif

#include <iostream>
#include <algorithm>
#include <utility>
using namespace std;

int P[10000+10];

void init(int N){
	for(int i=0;i<=N;++i) P[i]=i;
}
int root(int a){
	if(P[a]==a)return a;
	else return(P[a]=root(P[a]));
}
bool is_same_set(int a,int b){
	return root(a)==root(b);
}
void unite(int a,int b){
	P[root(a)]=root(b);
}
int main(){
	int N;
	cin>>N;
	int A[N][N];
	
	for(int i=0; i<N;i++){
		for(int j=0;j<N;j++){
			cin>>A[j][i]; //???????????\???
		}
	}

	int M = 0; 
	int cost[N*N],src[N*N],dst[N*N];
	for (int r=0; r<N;r++)
		for (int c=0; c<r;c++) //r<c???????§?????????????
			if (A[r][c] > -1) {
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				M += 1;
			}
	pair<int,int> edges[2000+100];
	for(int i=0;i<M;i++)
		edges[i]=make_pair(cost[i],i); //first???????????????second???ID
	sort(edges,edges+M);
	
	//for(int i=0;i<M;++i)
		//cout<<edges[i].first<<endl;

	init(N);
	int sum=0;
	for(int i=0;i<M;i++){
		if(is_same_set(src[edges[i].second],dst[edges[i].second])==0){
			unite(src[edges[i].second],dst[edges[i].second]);
			sum+=edges[i].first;
		}
	}
		cout<<sum<<endl;
}