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 <cstdio>
#include <cstring>
#define MAXN (1 << 21)
int g[101][101], d[101], n;
bool vis[101];

int mst()
{
  int sum = 0;
  d[0] = 0;
  for (int j = 0; j < n; j++)
  {
    int u = -1;
    int mini = MAXN;
    for (int i = 0; i < n; i++) // take node from V-T to T
    {
      if (d[i] < mini && !vis[i])
      {
        u = i;
        mini = d[i];
      }
    }
    if (u == -1) return -1;
    sum += mini;
    vis[u] = true;
    for (int v = 0; v < n; v++) // update smallest weight
    {
      if (!vis[v] && g[u][v] >= 0 && d[v] > g[u][v])
      {
        d[v] = g[u][v];
      }
    }
  }
  return sum;
}

int main()
{
  memset(vis, false, sizeof(vis));
  scanf("%d", &n);
  for (int i = 0; i < n; i++)
  {
    d[i] = MAXN;
  }
  for (int i = 0; i < n; i++)
  {
    for (int j = 0; j < n; j++)
    {
      scanf("%d", &g[i][j]);
    }
  }
  printf("%d\n", mst());
}

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

#define N 101
#define INF 2010
int n;

int A[N][N];
int color[N];
int d[N];

int mst(int root) {
    int totalW = 0;
    d[root] = 0;

    while(true) {
        int added = -1;
        int minw = INF;
        for (int i = 0; i < n; i++) {
            if (color[i] == 0 && d[i] < minw) {
                added = i;
                minw = d[i];
            }
        }

        if (added == -1) {
            break;
        }

        totalW += minw;
        color[added] = 1;
        for (int i = 0; i < n; i++) {
            if (color[i] == 0 && A[added][i] < d[i]) {
                d[i] = A[added][i];
            }
        }
    }

    return totalW;
}

int main() {
    cin >> n;

    int w;
    for (int i = 0; i < n; i++) {
        color[i] = 0;
        d[i] = INF;
        for (int j = 0; j < n; j++) {
            cin >> w;
            if (w == -1) A[i][j] = INF;
            else A[i][j] = w;
        }
    }

    cout << mst(0) << endl;

    return 0;
}

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

int x[10000][10000];
int MIN[10000];
int MINX = 0;
int MINZ = 10000000;

int main() {
	memset(MIN, 127, sizeof(MIN));
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
	for(int i=0;i<n;i++){
	    for(int j=0;j<n;j++){
	        if(x[i][j]!=-1){
	            MIN[i]=min(x[i][j],MIN[i]);
	        }
	    }
	}
	for(int i=0;i<n;i++){
	    MINX=0;
	    for(int j=0;j<n;j++){
	        MINX += MIN[j];
	    }
	    MINX -= MIN[i];
	    MINZ=min(MINZ,MINX);
	}
	cout<<MINZ<<endl;
	return 0;
}

C++: #define  _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <stdio.h>
#define INF 20000202
#define maxn 101
using namespace std;

int M[maxn][maxn] = {}, d[maxn] = {}, p[maxn] = {}, s[maxn] = {};
int n;

void Prim()
{
	for (int i = 0; i < n; i++)
		d[i] = INF;
	d[0] = 0;
	p[0] = -1;
	while (true)
	{
		int u = -1, mincost = INF;
		for(int i=0;i<n;i++)
			if (s[i] == 0 && d[i] < mincost)
			{
				mincost = d[i];
				s[i] = 1;
				u = i;
			}
		if (u == -1)break;
		for(int v=0;v<n;v++)
			if (M[u][v] != -1 && M[u][v] < d[v] && s[v] == 0)
			{
				d[v] = M[u][v];
				p[v] = u;
			}
	}
}

int main()
{
	int sum = 0;
	scanf("%d", &n);
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			scanf("%d", &M[i][j]);
	Prim();
	for (int i = 0; i < n; i++)
	{
		sum += d[i];
	}
	printf("%d", sum);
	return 0;
}

C++: #include<iostream>
#include<algorithm>
#define INF 99999
using namespace std;

int G[110][110] = {};

int prim(int n)
{
    int mini[110];
    int used[110];

    //init
    for(int i = 0;i < n;i++){
        mini[i] = INF;
        used[i] = 0;
    }
    mini[0] = 0;
    int ans = 0;

    while(true)
    {
        int v = -1;
        for(int i = 0;i < n;i++){
            if(!used[i] && (v == -1 || mini[i] < mini[v])) v = i;
        }
        if(v == -1) break;
        //ans = -1;

        used[v] = 1;
        ans += mini[v];
        //cout << ans << endl;

        for(int i = 0;i < n;i++){
            mini[i] = min(mini[i], G[v][i]);
        }
    }
    return ans;
}

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

    for(int i = 0;i < n;i++){
        for(int j = 0;j < n;j++){
            int cost;
            cin >> cost;
            if(cost == -1) G[i][j] = INF;
            else G[i][j] = cost;
        }
    }

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