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> 
#include<vector>
#include<algorithm>
#include<map>
#include<iomanip>
#include<set>
#include<queue>
#include<deque>
#include<iomanip>
#include<sstream>
#include<cmath>
#include<bitset>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(int i = n -1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
typedef long long int ll;
typedef long double ld;
const ll INF = (1 << 29);
ll h, m, n; string s;
const ll MOD= 1000000007;
const ld PI = acos(-1);
ll sum = 0;
template<typename A, size_t N, typename T>
void Fill(A(&array)[N], const T & val) {
    std::fill((T*)array, (T*)(array + N), val);
}int a[110][101];
int prim() {
    vector<int> d(110, INF), p(110, -1),co(110,0);
    d[0] = 0; int u, miv = 0;
    while (1) {
        miv = INF;
        u = -1;
        rep(i, n) {
            if (miv > d[i] && co[i] != 2) {
                u = i; miv = d[i];
            }
        }
        if (u == -1) break;
        co[u] = 2;
        rep(v, n) {
            if (co[v] != 2 && a[u][v] != INF) {
                if (d[v] > a[u][v]) {
                    d[v] = a[u][v];
                    p[v] = u; co[v] = 1;
                }
            }
        }
    }
    rep(i, n) {
        if (p[i] != -1) sum += a[i][p[i]];
    }return sum;
}
int main() {
    cin >> n; 
    rep(i, n) {
        rep(j, n) {
            cin >> a[i][j];
            if (a[i][j] == -1) {
                a[i][j] = INF;
            }
        }
    }
    cout << prim() << endl;
}

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

#define MAX 100
#define INF 2097152
#define WHITE 0
#define GRAY 1
#define BLACK 2

int n, M[MAX][MAX];

int main(void){

	int i,j,f;
	int n,u,v,minv,d[MAX],p[MAX],color[MAX],sum=0;
	scanf("%d",&n);
  
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			scanf("%d",&f);
			if(f == -1){
				M[i][j] = INF;
			}else{
				M[i][j] = f;
			}
		}
	}


	for(i=0;i<n;i++){
		d[i] = INF;
		p[i] = -1;
		color[i] = WHITE;
	}

	d[0] = 0;

	while(1){
		minv = INF;
		u = -1;
		for(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(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;
				}
			}
		}
	}

	for(i=0;i<n;i++){
		if(p[i] != -1){ 
			sum+= M[i][p[i]];
		}
	}

	printf("%d\n",sum);


return 0;

}

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

const int MAX = 100;

int count(bool check[MAX], int graph[MAX][MAX], int n,int i) {
	check[i] = true;
	int sum = 0;
	for (int j = 0; j < n; j++) {
		if (graph[i][j] != -1 && check[j] == false) {
			sum += count(check,graph, n, j);
			sum += graph[i][j];
		}
	}
	return sum;
}

int main() {
	int n;
	int g;
	int graph[MAX][MAX];

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

	//?§????
	for (int s = 0; s < n; s++) {
		//?????±???
		for (int m = 0; m < n; m++) {
			if (graph[s][m] == -1)continue;
			//??????
			for (int e = 0; e < n; e++) {
				if (graph[s][e] == -1 || graph[m][e] == -1)continue;
				if (graph[s][e] > graph[s][m] + graph[m][e]) {
					graph[s][e] = -1;
				}
			}
		}
	}

	bool check[MAX] = { false };
	cout << count(check, graph, n, 0);
	return 0;
}

C++: #include<stdio.h>
  
#define MAX 100
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define NIL -1
#define INF 100000

int n,G[MAX][MAX];

int prim(){
  int u,mincost,i;
  int d[MAX],pi[MAX],color[MAX];
  
  for( u = 0 ; u < n ; u++ ){
    d[u] = INF;
    pi[u] = NIL;
    color[u] = WHITE;
  }
  
  d[0] = 0;
  
  while(1){
    mincost = INF;
    i = NIL;
    for( u = 0 ; u < n ; u++ ){
      if(color[u] != BLACK && d[u] < mincost){
    i = u;
    mincost = d[u];
      }
    }
  
    if( i == NIL ) break;
  
    color[i] = BLACK;
  
    for( u = 0 ; u < n ; u++ ){
      if(color[u] != BLACK && G[i][u] != INF ){
    if( d[u] > G[i][u] ){
      d[u] = G[i][u];
      pi[u] = i;
      color[u] = GRAY;
    }
      }
    }
  }
  
  int sum = 0;
  
  for( u = 0 ; u < n ; u++ ){
    if( pi[u] != NIL ) sum += G[u][pi[u]];
  }
  
  return sum;
} 

  
int main(){
  int i,j,m;
  scanf("%d",&n);
  
  for( i = 0 ; i < n ; i++ ){
    for( j = 0 ; j < n ; j++ ){
      scanf("%d",&m);
      if(m==NIL) G[i][j]=INF;
      else G[i][j]=m; 
    }
  }
  
  printf("%d\n",prim());
  
  return 0;
}