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>
//#include"UnionFind.hpp"
using namespace std;



class UnionFind{
    int N;
    vector<int> par;
    vector<int> rank;
    public:
    UnionFind(int N):N(N),par(N),rank(N,0){iota(par.begin(),par.end(),0);}
    int find(int x);
    void unite(int x,int y);
    bool same(int x,int y){return find(x)==find(y);}
};

int UnionFind::find(int x){
    if(par[x]==x) return x;
    return par[x]=find(par[x]);
}
void UnionFind::unite(int x,int y){
    x=find(x),y=find(y);
    if(x==y) return;
    if(rank[x]>=rank[y]){
        if(rank[x]==rank[y]) rank[x]++;
        par[y]=x;
    }else{
        par[x]=y;
    }
}

using Weight=long long;
struct Edge{
    int from,to;
    Weight weight;
};
bool operator<(const Edge& lhs,const Edge& rhs){
    return lhs.weight<rhs.weight;
}

using Edges=vector<Edge>;
using Graph=vector<Edges>;


Edges MinimumSpanningTree(int n,Edges edges){
    Edges res;
    UnionFind u(n);
    for(int i=0;i<edges.size();i++){
        if(!u.same(edges[i].from,edges[i].to)){
            res.push_back(edges[i]);
            u.unite(edges[i].from,edges[i].to);
        }
    }
    return res;
}

Edges MinimumSpanningTree(const Graph& g){
    Edges edges;
    for(int i=0;i<g.size();i++){
        copy(g[i].begin(),g[i].end(),back_inserter(edges));
    }
    auto res=MinimumSpanningTree(g.size(),edges);
    return res;
}

int main(){
    int n;
    cin>>n;
    Graph g(n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            Weight c;
            cin>>c;
            if(i==j) continue;
            g[i].push_back({i,j,c});
        }
    }
    auto mst=MinimumSpanningTree(g);
    cout<<accumulate(mst.begin(),mst.end(),Weight(0),[](const Weight& lhs,const Edge& rhs){return lhs+rhs.weight;})<<endl;
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
int main()
{
    int n, inf = 10000000;
    scanf("%d", &n);
    vector<vector<int>> a(n, vector<int>(n));
    for (int i = 0; i < n; i++)
    {
        for (int j = 0, k; j < n; j++)
        {
            scanf("%d", &k);
            a[i][j] = k == -1 ? inf : k;
        }
    }
    
    vector<int> cost(n, inf);
    vector<bool> vis(n, false);
    cost[0] = 0;
    for (int mi = inf, u = 0; ; mi = inf)
    {
        for (int i = 0; i < n; i++)
        {
            if (!vis[i])
            {
                if (cost[i] < mi)
                {
                    mi = cost[i];
                    u = i;
                }
            }
        }
        if (mi == inf)
        {
            break;
        }
        vis[u] = true;
        for (int i = 0; i < n; i++)
        {
            if (!vis[i] && a[u][i] != -1)
            {
                cost[i] = min(cost[i], a[u][i]);
            }
        }
    }
    printf("%d\n", accumulate(cost.begin(), cost.end(), 0));
}

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

class Edge {
public:
	int v1, v2, d;
};

int n, k=0, V[100];
Edge E[5000];

void Sort() {
	for (int i = 1; i < k; i++) {
		Edge v = E[i];
		int j = i - 1;
		while (j >= 0 && E[j].d > v.d) {
			E[j + 1] = E[j];
			j--;
		}
		E[j + 1] = v;
	}
}

int Kruskal() {
	int m = 0;
	for (int i = 0; i < k; i++) {
		Edge e = E[i];
		if (V[e.v1] != V[e.v2]) {
			int v = V[e.v1], u = V[e.v2]; m += e.d;
			for (int j = 0; j < n; j++) {
				if (V[j] == u) V[j] = v;
			}
		}
	}
	return m;
}

int main() {
	int g;
	cin >> n;
	for (int i = 0; i < n; i++) {
		V[i] = i;
		for (int j = 0; j < n; j++) {
			cin >> g;
			if (i < j && g > -1) {
				E[k].v1 = i; E[k].v2 = j; E[k].d = g; k++;
			}
		}
	}

	Sort();

	cout << Kruskal() << endl;
}