Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

const (
	MAX_N      = 200
	MAX_WEIGHT = 2000
)

type Edge struct {
	start  int
	end    int
	weight int
}

type ShortestInfo struct {
	edges    []Edge
	shortest int
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	shortestList := make([]ShortestInfo, n)
	for i := 1; i < n; i++ {
		shortestList[i] = ShortestInfo{edges: []Edge{}, shortest: MAX_N*MAX_WEIGHT + 1}
	}

	adjacentMatrix := make([][]int, n)
	for i := 0; i < n; i++ {
		adjacentMatrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			v, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjacentMatrix[i][j] = v
		}
	}

	mst([]int{1}, shortestList, adjacentMatrix)
	fmt.Println(calculateMinWeight(shortestList))
}

func calculateMinWeight(shortestList []ShortestInfo) int {
	visitedList := make([]bool, len(shortestList))
	visitedList[0] = true
	sumWeight := 0
	for !visitedAll(visitedList) {
		shortestInfo := shortestList[0]
		shortestList = shortestList[1:]
		edges := shortestInfo.edges
		for _, edge := range edges {
			if !visitedList[edge.end-1] {
				visitedList[edge.end-1] = true
				sumWeight += edge.weight
			}
		}
	}
	return sumWeight
}

func visitedAll(visitedList []bool) bool {
	for _, v := range visitedList {
		if !v {
			return false
		}
	}
	return true
}

func mst(nodeStack []int, shortestList []ShortestInfo, adjacentMatrix [][]int) {
	for len(nodeStack) > 0 {
		currentNode := nodeStack[0]
		nodeStack = nodeStack[1:]
		currentShortest := getShortest(currentNode, shortestList)
		adjacents := findAdjacents(currentNode, adjacentMatrix)
		for i := 0; i < len(adjacents); i++ {
			adj := adjacents[i]
			s := getShortest(adj.end, shortestList)
			if currentShortest.shortest+adj.weight < s.shortest || (currentShortest.shortest+adj.weight == s.shortest && len(currentShortest.edges)+1 > len(s.edges)) {
				setShortest(adj.end, adj, currentShortest, shortestList)
				nodeStack = append(nodeStack, adj.end)
			}
		}
	}
}

func getShortest(node int, shortestList []ShortestInfo) ShortestInfo {
	return shortestList[node-1]
}

func setShortest(node int, edge Edge, currentShortest ShortestInfo, shortestList []ShortestInfo) {
	newEdges := make([]Edge, len(currentShortest.edges)+1)
	for i := 0; i < len(newEdges)-1; i++ {
		newEdges[i] = currentShortest.edges[i]
	}
	newEdges[len(newEdges)-1] = edge
	shortestInfo := ShortestInfo{edges: newEdges, shortest: currentShortest.shortest + edge.weight}
	shortestList[node-1] = shortestInfo
}

func findAdjacents(currentNode int, adjacentMatrix [][]int) []Edge {
	adjacents := adjacentMatrix[currentNode-1]
	edges := []Edge{}
	for i, v := range adjacents {
		if v > 0 {
			edges = append(edges, Edge{start: currentNode, end: i + 1, weight: v})
		}
	}
	return edges
}

func nextInt(sc *bufio.Scanner) (int, error) {
	sc.Scan()
	return strconv.Atoi(sc.Text())
}

C++: #include <iostream>
#include <climits>
#include <vector>
#include <algorithm>

using namespace std;

class UnionFind {
private:
  std::vector<int> data;
public:
  UnionFind(const int size):data(size,-1){}
  void union_set(int x, int y){
    x = this->get_root(x);
    y = this->get_root(y);
    
    if (x != y) {
      if (this->data[y] < data[x]) {
        swap(x, y);
      }
      this->data[x] += this->data[y];
      this->data[y] = x;
    }  
  }
  bool is_same(const int x, const int y){
    return this->get_root(x) == this->get_root(y);
  }
  int get_root(const int x){
    return this->data[x] < 0 ? x : this->data[x] = this->get_root(this->data[x]);
  }
  int get_size(int x){
    return -this->data[this->get_root(x)];
  }
};

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

struct Graph{
  int v_size;
  vector<Edge> edge_set;
  
  Graph(const int v_size):v_size(v_size){}
  
  void add_edge(const int s, const int t, const int w){
    this->edge_set.emplace_back(Edge{s, t, w});
  }
};

int mst(Graph& g){
  UnionFind uf(g.v_size);
  int ans {0};

  sort(begin(g.edge_set), end(g.edge_set));

  for(auto&& e : g.edge_set){
    if(!uf.is_same(e.from, e.to)){
      ans += e.cost;
      uf.union_set(e.from, e.to);
    }
  }
  
  return ans;
}

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

  int x;
  for(int i = 0; i < n; ++i){
    for(int j = 0; j < n; ++j){
      cin >> x;
      if(x != -1){
        g.add_edge(i, j, x);
      }
    }
  }

  cout << mst(g) << endl;
}

C++: #include <iostream>
#include <sstream>
#include <cstdio>
#include <stdlib.h>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
#define max 2001
#define INF 200000000
int color[max],p[max],n;
int m[max][max],d[max];
void prim(){
  int mincost,u,i;
  p[0]=-1;
  for(i=1;i<n;i++)d[i]=INF;
  while(1){
    mincost = INF;
    for(i=0;i<n;i++){
      if(color[i]!=1&&d[i]<mincost){
	mincost=d[i];
	u=i;
      }
    }
    if(mincost==INF)break;
    color[u]=1;
    for(int j=0;j<n;j++){
      if(color[j]!=1&&m[u][j]!=-1)
	if(m[u][j]<d[j]){
	  d[j]=m[u][j];
	  p[j]=u;
	  color[j]=-1;
	}
    }
  }
}
int main(){
  int sum=0;
  cin>>n;
  for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
      cin>>m[i][j];
  prim();
  for(int i=0;i<n;i++)
    sum+=d[i];

  cout<<sum<<endl;
  return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
//#include "MyMath.h"
//#include "MyDisjointset.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <functional>
#include <stdio.h>
using namespace std;
typedef pair<int, int> P;
const int INF = 2000000000;
int main() {
	int n; cin >> n;
	int m[101][101];
	for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)
		cin >> m[i][j];
	int res = 0;
	int *d = new int[n];
	fill(d, d + n, INF); 
	d[0] = 0;
	bool *visit = new bool [n];
	priority_queue <P, vector<P>, greater<P> > q;
	q.push(P(d[0], 0));
	while (!q.empty()) {
		int f = q.top().first, s = q.top().second;
		visit[s] = true;
		res += f;
		q.pop();
		for (int i = 0; i < n; i++)
			if (!visit[i] && m[s][i] != -1 && m[s][i] > d[i]) {
				m[s][i] = d[i];
				q.push(P(d[i], i));
			}
	}
	cout << res << endl;
	delete[] d, visit;
	return 0;
}