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 <bits/stdc++.h>
using namespace std;

static const int N = 100;
static const int INF = (1 << 30);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;


int n;
int m[N][N];

int prim(){
    int u,min_val;
    int d[N],p[N],color[N];

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

    d[0] = 0;
    while(1){
        min_val = INF;
        u = -1;
        for(int i=0;i<n;i++){
            if(min_val > d[i] && color[i] != BLACK){
                u = i;
                min_val = d[i];
            }
        }

        if(u == -1) break;
        color[u] = BLACK;
        for(int 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;
                }
            }
        }
    }

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

    return sum;
}


//mainは問題なし
int main(){
    int in_val;
    cin >> n;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin >> in_val;
            if(in_val == -1)
                in_val = INF;
            m[i][j] = in_val;
        }
    }

    cout << prim() << endl;

}

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

const static int MAX = 100;
const static int INFTY = (1<<21);
const static int WHITE = 0;
const static int GRAY = 1;
const static 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(true){
    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 work;
      cin >> work;
      M[i][j] = (work == -1) ? INFTY : work;
    }
  }

  cout << prim() << endl;


  return 0;
}

C++: #include <iostream>
#include <queue>
#define INF 200000
using namespace std;
typedef pair<int,int> P;
P a;
priority_queue< P,vector<P> ,greater<P> > pq;
int map[101][101];
bool decided[101];
int sum,n;
int node,count;
void check(){
	node=1;
	decided[node]=true;
	count=n-1;
	while(1){
		for(int i=1;i<=n;i++){
			if(map[node][i]!=-1&&!decided[i]){
				a=make_pair(map[node][i],i);
				pq.push(a);
			}
		}
		while(decided[pq.top().second])pq.pop();
		sum+=pq.top().first;
		node=pq.top().second;
		decided[node]=true;
		count--;
		if(count==0)break;
		pq.pop();
	}
}

int main(){
	cin >>n;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin >> map[i][j];
		}
	}
	sum=0;
	check();
	cout << sum<<endl;
}