Go: package main

import (
	"sort"
	"bufio"
	"os"
	"fmt"
	"strconv"
)

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

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;
}