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;

const int MAX = 100;
const int INFINITY = 2 << 21;
int n;
int G[MAX][MAX];
int distances[MAX];
int parents[MAX];
int states[MAX];

int prim() {
  int id = 0;
  distances[id] = 0;

  while (1) {
    int min = INFINITY;

    for (int i = 0; i < n; i++) {
      if (states[i] == 0 && distances[i] < min) {
        min = distances[i];
        id = i;
      }
    }

    if (min == INFINITY) break;

    for (int i = 0; i < n; i++) {
      if (states[i] != 0 || G[id][i] == -1) continue;
      if (G[id][i] < distances[i]) {
        distances[i] = G[id][i];
        parents[i] = id;
      }
    }

    states[id] = 1;
  }

  int sum = 0;
  for (int i = 0; i < n; i++) {
    if (parents[i] != -1) sum += distances[i];
  }
  return sum;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n;

  for (int i = 0; i < n; i++) {
    distances[i] = INFINITY;
    parents[i] = -1;
    states[i] = 0;
    for (int j = 0; j < n; j++) {
      cin >> G[i][j];
    }
  }

  cout << prim() << endl;
  return 0;
}

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

int n;
int a[101][101];
int flg[101];
int t[101];
int sum = 0;

void visit(){
  int ima = 0;
  int mine = 100000000;
  
  
  for(int k=0;k<n-1;k++) {
    mine = 10000000;
    for(int i=0;i<n;i++) {
      if(flg[i] == 0 && mine > t[i]) {
	mine = t[i];
	ima = i;
      }
    }
    sum += mine;
    flg[ima] = 1;
    
    for(int i=0;i<n;i++) 
      if(a[ima][i] != -1) 
	if(t[i] > a[ima][i] ) t[i] = a[ima][i];
    
    
  }
}

int main() {

  cin >> n;

  for(int i=0;i<n;i++) 
    for(int j=0;j<n;j++) 
      cin >> a[i][j];
  
  for(int i=0;i<n;i++) {
    flg[i] = 0;
    t[i] = 100000000;
  }
  
  t[0] = 0;
  flg[0] = 1;
  for(int i=0;i<n;i++) 
    if(a[0][i] != -1) t[i] = a[0][i];

  visit();

  cout << sum << endl;
 
  return 0; 
  
}

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

int n;
int g[101][101];

int d[101];
char c[101];
int p[101];

void prim() {
    for (int i = 0; i < n; ++i) {
        d[i] = INT_MAX;
        c[i] = 'w';
    }
    c[0] = 'b';
    d[0] = 0;
    while (true) {
        int u, v;
        int mine = INT_MAX;
        for (int j = 0; j < n; ++j) {
            if (c[j] == 'b') {
                u = j;
                for (int k = 0; k < n; ++k) {
                    if(g[u][k] > -1 && g[u][k] <= d[k] && c[k] != 'b' && g[u][k] <= mine) {
                        d[k] = g[u][k];
                        mine = d[k];
                        v = k;
                    }
                }
            }
        }
        p[v] = u;
        c[v] = 'b';
        if(mine == INT_MAX) break;
    }
}

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int w;
            cin >> w;
            g[i][j] = w;
        }
    }
    prim();
    int sum;
    for (int k = 0; k < n; ++k) {
        sum += d[k];
    }
    cout << sum << endl;


    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>

using namespace std;

struct edge {
    int from, to, cost;
};

int main() {
    int n;
    cin >> n;

    vector<edge> E;
    int cost;
    for (int i=0; i<n; ++i) {
        for (int j=0; j<n; ++j) {
            cin >> cost;
            if (0 <= cost) {
                E.push_back((edge){ i, j, cost });
            }
        }
    }

    bool used[100] = {};
    used[0] = true;

    int ret = 0;

    while (1) {
        int next = -1;
        int min_cost = INT_MAX;
        for (int i=0; i<(int)E.size(); ++i) {
            edge &e = E[i];
            if (used[e.from] && ! used[e.to] && e.cost < min_cost) {
                next = e.to;
                min_cost = e.cost;
            }
        }
        if (next == -1) break;
        used[next] = true;
        ret += min_cost;
    }

    cout << ret << endl;

    return 0;
}

C++: #include<stdio.h>
#include<algorithm>
#include<queue>
#include<string.h>
using namespace std;
#define NIL -2000000001
#define INFTY 2000000001
#define MAX 101
#define WHITE 0
#define GRAY 1
#define BLACK 2

int n = 0;
int adm[MAX][MAX];
int color[MAX];
int d[MAX], p[MAX];
queue<int> queueBfs;


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

  while (true) {
    int mincost = INFTY;
    int u; //訪問する頂点

    for (int i = 0; i < n; i++) {
      if (color[i] != BLACK && d[i] < mincost) {
        mincost = d[i];
        u = i;
      }
    }
    if (mincost == INFTY) break;
    sum += mincost;
    color[u] = BLACK;

    // u周りの頂点vの情報を入れる
    for (int v = 0; v < n; v++) {
      if (color[v] != BLACK && adm[u][v] != -1 && adm[u][v] < d[v]) {
        d[v] = adm[u][v];
        p[v] = u;
        color[v] = GRAY;
      }
    }
  }

  return sum;
}

int main() {
  scanf("%d", &n);
  for ( int i = 0; i < n; i++ ) {
    for ( int j = 0; j < n; j++) {
      scanf("%d", &adm[i][j]);
    }
  }

  printf("%d\n", mst());
  
  return 0;
}