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<stdio.h>
//#include<cstdlib>
// 0origin

#define MAX 100
#define INF 2001
#define WHITE 0
#define BLACK 1

int n;

// calculate the minimum cost
int PrimMST(int a[MAX][MAX]){ //refered to http://www.deqnotes.net/acmicpc/prim/#a1
    int v,i,j = 0, color[MAX], mincost, sumcost = 0, connected;
    
    for (i = 0; i < n; i++) {
        color[i] = WHITE;
    }
    
    color[0] = BLACK;
    while (j < n-1){
        
        mincost = INF;
        connected = INF;
        for (v = 0; v < n; v++) {
            if(color[v] == WHITE){
                continue;
            }
            for (i = 0; i < n; i++) {
                //printf("color[%d] : %s, cost %d to %d : %d\n", i, color[i] == 1 ? "BLACK" : "WHITE", v, i, a[v][i]);
                if (color[i] == WHITE && mincost > a[v][i]) {
                    mincost = a[v][i];
                    connected = i;
                    //printf("  min is rewritten : %d\n", mincost);
                }
            }
        
        }
        //printf("\nfin:%d\n\n", mincost);
        sumcost += mincost;
        color[v] = BLACK;
        if (connected != INF) {
            color[connected] = BLACK;
        }
        
        j++;
        
    }
    return sumcost;
}

int main(){
    int i, j, a[MAX][MAX];
    
    scanf("%d", &n);
    
    //printf("\n\n\n");
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){
            scanf("%d", &a[i][j]);
            if(a[i][j] == -1){
                a[i][j] = INF;
            }
            //printf(" %4d", a[i][j] != INF ? a[i][j] : -1);
        }
        //printf("\n");
    }
    
    printf("%d\n", PrimMST(a));
    
    return 0;
}

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;
	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() {
	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;
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;
  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() {
  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;
int map[101][101];
int dp[101];
bool decided[101];
int sum,n;
int node,nextnode,mincost;
void check(){
	node=1;
	decided[node]=true;
	dp[node]=0;
	while(1){
		nextnode=-1;
		mincost=20000;
		dp[node]=0;
		for(int i=1;i<=n;i++){
			if(map[node][i]==-1||decided[i])continue;

			if(dp[i]==-1){
				dp[i]=map[node][i]+dp[node];
			}else{
				dp[i]=min(dp[i],map[node][i]+dp[node]);
			}
			if(mincost>dp[i])nextnode=i;
		}
		if(nextnode==-1)break;
		sum+=map[node][nextnode];
		decided[nextnode]=true;
		node=nextnode;
	}
}

int main(){
	cin >>n;
	for(int i=1;i<=n;i++){
		dp[i]=-1;
	}

	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin >> map[i][j];
		}
	}

	check();
	cout << sum<<endl;
}

C++: #include<iostream>
#define MAX 100
#define INF (2<<29)
using namespace std;
int main(){
  int n;
  cin>>n;
  int graph[MAX][MAX];
  
  for(int i=1;i<n+1;i++){
    for(int j=1;j<n+1;j++){
      cin>>graph[i][j];
      if(graph[i][j]==-1)graph[i][j]=INF;
    }
  }
  
  int visited[MAX];
  int min[MAX];
  for(int i=1;i<n+1;i++){
    visited[i]=0;
    min[i]=INF;
  }
  
  min[1]=0;
  int ans=0;
  while(true){
    int a=-1;
    for(int i=1;i<n+1;i++){
      if(visited[i]==0&&(a==-1||min[i]<min[a]))a=i;
    }

    if(a==-1)break;
    visited[a]=1;
    ans +=min[a];

    for(int i=1;i<n+1;i++){
      min[i]=min[i]<graph[a][i] ? min[i]:graph[a][i];
    }
  }
  cout<<ans<<endl;
  return 0;
}