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);

enum Color {
  WHITE, GRAY, BLACK
};

int M[MAX][MAX];
int d[MAX];
int p[MAX];
Color color[MAX];
int n;

void init() {
  for (int i = 0; i < n; i++) {
    color[i] = WHITE;
    d[i] = INFTY;
  }
}

void prim() {
  init();
  d[0] = 0;
  p[0] = -1;

  while (true) {
    int mincost = INFTY;
    int u;
    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 (M[u][v] != -1 && color[v] != BLACK) {
        if (M[u][v] < d[v]) {
          d[v] = M[u][v];
          p[v] = u;
          color[v] = GRAY;
        }
      }
    }
  }
}

int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> M[i][j];
    }
  }
  prim();
  int result = 0;
  for (int i = 0; i < n; i++) {
    result += d[i];
  }
  cout << result << endl;
  return 0;
}

C++: #include <iostream>
using namespace std;
#define N 100
static const int white=0;
static const int gray=1;
static const int black=2;
static const int infty=(1<<21);

int n,M[N][N];

int prim(){
    int u,minv;
    int d[N],p[N],color[N];
    
    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<cstdio>
#include<string>
#include<algorithm>
#include<cstring>
using namespace std;
#define int(x) int x; scanf("%d",&x)
#define input(x) scanf("%d",&x)
#define rep(x,n) for(int x = 0; x < n; x++)
#define _br printf("\n")
#define INF 2000000000

bool complete[100];
int d[100];

int rec_msp(int n, int Path[][100]){
    int moP = 0;
    rep(i,n){
        complete[i] = false;
        d[i] = INF;
    }
    d[0] = 0;
    int num = 0;
    
    
    while (num != n) {
    
        int mind = INF;
        int mindi = 0;
        rep(i,n){
            if (mind > d[i] && !complete[i]) {
                mind = d[i];
                mindi = i;
            }
        }
        
        complete[mindi] = true;
        num++;
        
        //update d[] with mindi.
        
        rep(i,n){
            if (Path[mindi][i] != -1 && d[i] > Path[mindi][i] && !complete[i]) {
                d[i] = Path[mindi][i];
            }
        }
        
    }
    
    int sum = 0;
    rep(i,n) sum += d[i];
    
    return sum;
}

int main(){
    int(n);
    int Path[100][100];
    rep(r,n){
        rep(c,n) input(Path[r][c]);
    }
    
    printf("%d\n",rec_msp(n,Path));
    
    return 0;
}

C++: #include<iostream>
using namespace std;
#define N 105
#define INF 1<<21
int n;
int a[N][N];
int d[N],p[N],color[N];              //0.未访问的节点   1.正在访问的节点  2.已经访问过的节点 
int prim(){
	int u ,minv;
	for (int i = 0;i < n;i++){
		d[i] = INF;
		p[i] = -1;
		color[i] = 0; 
	}
	d[0] = 0;
	while (1){
		minv = INF;
		u = -1;
		for (int i = 0;i < n;i++){
			if (minv > d[i] && color[i] != 2){
				u = i;
				minv = d[i]; 
			}
		}
		if ( u == -1) break;
		color[u] = 2;
		for (int v = 0;v < n;v++){
			if (color[v] != 2 && a[u][v] != INF){
				if (d[v] > a[u][v]){
					d[v] = a[u][v];
					p[v] = u;
					color[v] = 1;
				}
			}
		}
	}
	int sum = 0;
	for (int i = 0;i < n;i ++){
		if (p[i] != -1){
			sum = sum + a[i][p[i]];
		}
	}
	return sum;
}

int main()
{
	cin >> n;
	int x;
	for (int i = 0;i < n;i++){
		for (int j = 0;j < n;j++){
			cin >> x;
			if (x == -1){
				a[i][j] = INF;
			}
			else{
				a[i][j] = x;
			}
		}
	}
	cout << prim() << endl;
	return 0;
}

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

int P[101];

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;
	init(n);
	int a[101][101];
	for(int i=0;i<n;i++)
	   for(int j=0;j<n;j++)
	       cin >> a[i][j];
	int M=0;
	int cost[10100],src[10100],dst[10100];
	for(int r=0;r<n;r++)
	   for(int c=r+1;c<n;c++)
	      if(a[r][c]>-1)
	      {
	      	cost[M]=a[r][c];
	      	src[M]=r;
	      	dst[M]=c;
	      	M++;
		  }
	pair<int,int> edges[10100];
	for(int i=0;i<M;i++)
	{
		edges[i].first=cost[i];
		edges[i].second=i;
	}
	sort(edges,edges+M);
	int sum=0;
	for(int i=0;i<M;i++)
	{
		if(is_same_set(src[edges[i].second],dst[edges[i].second]))
		  continue;
		unite(src[edges[i].second],dst[edges[i].second]);
		sum+=edges[i].first;
	}
	cout << sum << endl;
}

C++: #include <stdio.h>
#define MAX 100
#define INFTY 100000000
#define WHITE 0
#define BLACK 2
#define GRAY 1

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(){
    scanf("%d",&n);
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
            int e;
            scanf("%d",&e);
            M[i][j] = (e == -1) ? INFTY:e;
            
        }
    }
    printf("%d\n", prim());
    return 0;
}