Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] > 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A > edges[j].A })

	sum := 0
	for len(edges) > 0 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

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 a, min;
   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 ) {
      min = INFTY;
      u = -1;

      for ( int i = 0; i < n; i++ ) {
         if ( min > d[i] && color[i] != BLACK ) {
            a = i;
            min = d[i];
         }
      }

      if ( a == -1 ) break;
      color[a] = BLACK;
      for ( int v = 0; v < n; v++ ) {
         if ( color[v] != BLACK && M[a][v] != INFTY ) {
            if ( d[v] > M[a][v] ) {
               d[v] = M[a][v];
               color[v] = GRAY;
            }
         }
      }
   }

   int sum = 0;
   for ( int i = 0; i < n; i++ ) {
      if ( p[i] != -1 ) sum = 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;
#define N 100
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INFTY 10000

int n, M[N][N];


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

  while(true){
    mincost = INFTY;
    u = -1;
    //TとV-Tをつなぐ辺の中で最小のものを探す
    for(int i = 0 ; i < n ; i++){
      if(color[i] != BLACK && d[i] < mincost ){
        mincost = d[i];
        u = i;
      }
    }
    if(u == -1){
      break;
    }
    color[u] = BLACK;

    //Tの中の各頂点からのV-Tの頂点への最短辺の長さをd[v]に入れる
    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(){
  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;
    }
  }
  //int sum = prim();
  cout << prim() << "\n";
  return 0;

}

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

const int I_MAX = 0xfffffff;
const int MAX = 100;


int main() {
	int n;
	int graph[MAX][MAX];
	bool table[MAX] = { false };
	int sum = 0;

	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int temp;
			cin >> temp;
			if (temp == -1)temp = I_MAX;
			graph[i][j] = temp;
		}
	}

	table[0] = true;

	for (int i = 0; i < n - 1; i++) {
		int cost = I_MAX;
		int m;

		for (int j = 0; j < n; j++) {
			if (table[j] == false)continue;

			for (int k = 0; k < n; k++) {
				if (graph[j][k] < cost && table[k] == false) {
					cost = graph[j][k];
					m = k;
				}
			}
		}

		sum += cost;
		table[m] = true;
	}

	cout << sum << endl;

	return 0;
}

C++: 
#include<bits/stdc++.h>

using namespace std;

const int maxn=1e2+5;
const int inf=(1<<21);
const int white=0;
const int gray=1;
const int black=2;

int n,m[maxn][maxn];

int prim()
{
    int u,minv;
    int d[maxn],p[maxn],color[maxn];
    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()
{
    scanf("%d",&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;
}
/*
5
-1 2 3 1 -1
2 -1 -1 4 -1
3 -1 -1 1 1
1 4 1 -1 3
-1 -1 1 3 -1
*/

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, i;
    int d[MAX], q[MAX], color[MAX];
    
    for ( i = 0; i < n; i++ ) {
        d[i] = INFTY;
        q[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];
                    q[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    int sum = 0;
    for ( int i = 0; i < n; i++ ){
        if( q[i] != -1 ) sum += M[i][q[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;
}