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<algorithm>
#define MAXV 101
#define INF 2001
using namespace std;

int n, total = 0, mine, minj;
int mst[MAXV] = {}; //1 origin
int edge[MAXV][MAXV] = {}; //1 origin

void prim(void);
bool doesFinished(void);

int main() {
	int i, j;
	
	cin >> n;
	for (i = 1; i <= n; i++) {
		
		for (j = 1; j <= n; j++) {
			cin >> edge[i][j];
		}
	}

	mst[1] = 1;
	while (!doesFinished()) {
		prim();
	}

	cout << total << endl;

	return 0;
}

void prim(void) {
	int i, j;
	mine = INF;
	for (i = 1; i <= n; i++) {
		if (mst[i] == 0)continue;
		for (j = 1; j <= n; j++) {
			if (edge[i][j] == -1 || mst[j] == 1)continue;
			if (edge[i][j] < mine) {
				mine = edge[i][j];
				minj = j;
			}
		}
	}
	mst[minj] = 1;
	if(mine != INF)total += mine;
}

bool doesFinished(void) {
	for (int i = 1; i <= n; i++) {
		if (mst[i] == 0)return false;
	}
	return true;
}

C++: #include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <typeinfo>
#include <utility> 

#define rep(i,m,n) for(int i = m;i < n;++i)
using namespace std;
using ll = long long;
using R = double;
const ll inf = 1LL << 50;
const ll MOD = 1e9 + 7;

int infty = (1 << 21);
int cost[100][100];
int mincost[100];
bool used[100];
int V;

int prim() {
	for (int i = 0; i < V; ++i) {
		mincost[i] = infty;
		used[i] = false;
	}
	mincost[0] = 0;
	int res = 0;

	while (1) {
		int v = -1;
		for (int u = 0; u < V; u++) {
			if (!used[u] && (v == -1 || mincost[u] < mincost[v])) {
				v = u;
			}
		}
		if (v == -1)break;
		used[v] = true;
		res += mincost[v];

		for (int u = 0; u < V; u++) {
			mincost[u] = min(mincost[u], cost[v][u]);
		}
	}
	return res;
}


int main() {
	cin >> V;
	rep(i, 0, V)rep(j, 0, V) {
		int e; cin >> e;
		cost[i][j] = (e == -1) ? infty : e;
	}

	cout << prim() << endl;
}

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

struct Edge {
    int from, to, cost;
    Edge(int f, int t, int c) : from(f), to(t), cost(c) { }
    bool operator <(const Edge& e) const {
        return cost < e.cost;
    }
};

struct UnionFind {
    vector<int> data;
    UnionFind(int n) : data(n, -1) { }
    int root(int x) {
        return data[x] < 0 ? x : data[x] = root(data[x]);
    }

    bool same(int x, int y) {
        return root(x) == root(y);
    }

    void merge(int x, int y) {
        x = root(x), y = root(y);
        if(x != y) {
            data[x] += data[y]; data[y] = x;
        }
    }
};

int main() {
    int N; cin >> N;
    vector<Edge> es;
    for(int i = 0; i < N; i++) {
        for(int j = 0; j < N; j++) {
            int c; cin >> c;
            if(c != -1) {
                es.push_back(Edge(i, j, c));
            }
        }
    }
    sort(es.begin(), es.end());
    UnionFind uf(N);
    int ans = 0;
    for(int i = 0; i < (int)es.size(); i++) {
        int from = es[i].from;
        int to = es[i].to;
        int cost = es[i].cost;
        if(uf.same(from, to)) continue;
        uf.merge(from, to);
        ans += cost;
    }
    cout << ans << endl;
}

C++: #include<bits/stdc++.h>
using namespace std;

typedef pair< int , int > P;
struct Edge {
  int to,cost;
  Edge(){}
  Edge(int to,int cost):to(to),cost(cost){};
};
vector< vector< Edge > > Graph;
int V,E;
int prim(){
  int total = 0;
  vector< bool > used(Graph.size(),false);
  priority_queue< P,vector< P >,greater< P > > que;
  que.push(P(0,0));
  while(!que.empty()){
    int cost = que.top().first;
    int now = que.top().second;
    que.pop();
    if(used[now]) continue;
    used[now] = true;
    total += cost;
    for(int i=0;i<Graph[now].size();i++){
      que.push(P(Graph[now][i].cost,Graph[now][i].to));
    }
  }
  return total;
}

int main(){
  cin >> V;
  Graph.resize(V+1);
  /*
  for(int i=0;i<E;i++){
    int s,t,d;
    cin >> s >> t >> d;
    Graph[s].push_back(Edge(t,d));
    Graph[t].push_back(Edge(s,d));
    }*/
  for(int i=0;i<V;i++){
    for(int j=0;j<V;j++){
      int d; cin >> d;
      if(d != -1){
	Graph[i].push_back(Edge(j,d));
	Graph[j].push_back(Edge(i,d));
      }
    }
  }
  cout << prim() << endl;
}