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 <cmath>
#include <vector>
#include <string>
#include <algorithm>

constexpr int INF = 3000;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    int n, aij, mincost, minu, sum=0;
    std::cin >> n;
    std::vector<std::vector<int>> a(n);
    std::vector<int> d(n), p(n), color(n); // white:0, gray:1, black:2
    for (int i=0; i<n; i++) {
        for (int j=0; j<n; j++) {
            std::cin >> aij;
            a[i].push_back(aij);
        }
        d[i] = INF;
    }
    d[0]=0;
    p[0]=-1;
    while (true) {
        mincost = INF;
        for (int i=0; i<n; i++) {
            if (color[i] < 2 and d[i] < mincost) {
                mincost = d[i];
                minu = i;
            }
        }
        if (mincost == INF) {
            break;
        }
        color[minu] = 2;
        for (int v=0; v<n; v++) {
            if (color[v] < 2 and a[minu][v] >= 0 and d[v] > a[minu][v]) {
                d[v] = a[minu][v];
                p[v] = minu;
                color[v] = 1;
            }
        }
    }

    for (int i=0; i<n; i++) {
        sum += d[i];
    }
    std::cout << sum << "\n";

    return 0;
}

C++: #include <stdio.h>
#define rep(i, n) for(int i = 0; i < n; ++i)

int main(void) {
  int n, i, j, ans = 0;
  scanf("%d", &n);
  int a[n][n];
  char f[n];
  rep(i, n) rep(j, n) scanf("%d", &a[i][j]);
  rep(i, n) f[i] = 0;
  f[0] = 1;
  rep(i, n - 1) {
    int min = 10000, minx, miny;
    rep(j, n) {
      rep(k, n) {
        if(f[j] && !f[k] && a[j][k] > 0 && a[j][k] < min) min = a[j][k], minx = j, miny = k;
      }
    }
    ans += min;
    f[miny] = 1;
  }
  printf("%d\n", ans);
  return 0;
}

C++: #include <iostream>
#include <queue>
#include <utility>
#include <functional>
#include <vector>
using namespace std;
int cost[100][100];
int prim(int n,int s){
	typedef pair<int,int> P;
	bool ischeck[n];
	int mincost = 0;
	priority_queue<P,vector<P>,greater<P> > pq;
	P p,tp;
	for(int i = 0;i < n;++i){
		ischeck[i] = false;
		if(cost[s][i] != -1){
			p.first = cost[s][i];
			p.second = i;
			pq.push(p);
		}
	}
	ischeck[s] = true;
	while(!pq.empty()){
		p = pq.top();
		pq.pop();
		if(ischeck[p.second]) continue;
		else{
			ischeck[p.second] = true;
			mincost += p.first;
			for(int i = 0;i < n;++i){
				if(cost[p.second][i] != -1){
					tp.first = cost[p.second][i];
					tp.second = i;
					pq.push(tp);
				}
			}
		}
	}
	return mincost;
}
int main(){
	int n;
	cin >> n;
	for(int i = 0;i < n;++i){
		for(int j = 0;j < n;++j){
			cin >> cost[i][j];
		}
	}
	cout << prim(n,0) << endl;
}

C++: #include <stdio.h>
#include <limits.h>
int n,M[100][100];
int prim();
int main(){
  int i,j,w;
  scanf("%d",&n);
  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      scanf("%d",&w);
      if(w==-1)M[i][j]=INT_MAX;
      else M[i][j]=w;
    }
  }
  printf("%d\n",prim());
  return 0;
}
int prim(){
  int sum,i,u,mincost,C[100],d[100],p[100];
  for(i=0;i<n;i++){
    d[i]=INT_MAX;
    C[i]=0;
    p[i]=-1;
  }
  d[0]=0;
  while(1){
    u=-1;
    mincost=INT_MAX;
    for(i=0;i<n;i++){
      if(C[i]!=2&&d[i]<mincost){
        mincost=d[i];
        u=i;
      }
    }
    if(u==-1)break;
    C[u]=2;
    for(i=0;i<n;i++){
      if(C[i]!=2&&M[u][i]!=INT_MAX){
        if(d[i]>M[u][i]){
          d[i]=M[u][i];
          p[i]=u;
          C[i]=1;
        }
      }
    }
  }
  sum=0;
  for(i=0;i<n;i++){
    if(p[i]!=-1)sum+=M[i][p[i]];
  }
  return sum;
}