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 <iomanip>
#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <functional>
#include <sstream>
#include <string>
#include <utility>
#include <map>
#include <memory>
#include <set>
#include <vector>
#include <deque>
#include <list>
#include <stack>
#include <queue>
// #include <array>

using namespace std;

class MSTree
{
public:
  int solve();
};

int MSTree::solve()
{
  int n;
  cin >> n;
  
  vector<vector<int>> adj(n, vector<int>(n));
  list<int> t, vt;

  for ( auto i = 0; i < n; ++i )
    for ( auto j = 0; j < n; ++j )
      cin >> adj[i][j];

  t.push_back( 0 );

  for ( auto i = 1; i < n; ++i )
    vt.push_back( i );

  int w = 0;

  while ( vt.size() )
    {
      int mw = 4000;
      list<int>::iterator itm;
      
      for ( auto ita = t.begin(); ita != t.end(); ++ita )
        for ( auto itb = vt.begin(); itb != vt.end(); ++itb )
          {
            if ( adj[*ita][*itb] >= 0 && mw > adj[*ita][*itb] )
              {
                itm = itb;
                mw = adj[*ita][*itb];
              }
          }
      
      w += mw;
      t.push_back( *itm );
      vt.erase( itm );
    }

  cout << w << endl;
    
  return 0;
}

int main()
{
  MSTree m;

  m.solve();

  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<queue>
#include<utility>
#include<vector>

using namespace std;



int main() {
	int n,tmp;
	cin >> n;
	pair<int, pair<int, int>>* sorted_weight = new pair<int, pair<int, int>>[n * n];
	int* equiv = new int[n];


	int cnt_equiv = 0;
	int cnt_edge = 0;
	int cost = 0;
	
	for (int i = 0;i < n;i++) {
		for (int j = 0;j < n;j++) {
			cin >> tmp;
			sorted_weight[i * n + j] = make_pair(tmp, make_pair(i, j));
		}
		equiv[i] = 0;
	}
	sort(sorted_weight, sorted_weight + n * n);
	for (int i = upper_bound(sorted_weight, sorted_weight + n * n, make_pair(-1, make_pair(n, n))) - sorted_weight;cnt_edge<n-1;i++) {
		if (equiv[sorted_weight[i].second.second] == 0 || equiv[sorted_weight[i].second.first] == 0) {
			cnt_edge++;
			cost += sorted_weight[i].first;
			if (equiv[sorted_weight[i].second.second] == 0 && equiv[sorted_weight[i].second.first] == 0) {
				cnt_equiv++;
				equiv[sorted_weight[i].second.second] = equiv[sorted_weight[i].second.first] = cnt_equiv;
			}
			else if (equiv[sorted_weight[i].second.second] == 0) {
				equiv[sorted_weight[i].second.second] = equiv[sorted_weight[i].second.first];
			}
			else {
				equiv[sorted_weight[i].second.first] = equiv[sorted_weight[i].second.second];
			}
		}
		else if (equiv[sorted_weight[i].second.second] != equiv[sorted_weight[i].second.first]) {
			cnt_edge++;
			cost += sorted_weight[i].first;
			tmp = equiv[sorted_weight[i].second.second];
			for (int j = 0;j < n;j++) {
				if (equiv[j] == tmp)equiv[j] = equiv[sorted_weight[i].second.first];
			}
		}
	}
	
	cout << cost << endl;
}

C++: #include <stdio.h>
#define INF 100000000
#define BLACK 0
#define WHITE 1
#define N 101
 
int n,a[N][N];

int prim(void)
{
  int u,v,i,mincost,d[N],pi[N],total = 0,color[N];
 
  for(u = 1;u <= n;u++){
    d[u] = INF;
    pi[u] = -1;
    color[u] = WHITE;
  }
 
  d[1] = 0;
     
  while(1){
    mincost = INF;
    for(i = 1;i <= n;i++){
      if(color[i] != BLACK && d[i] < mincost){
	mincost = d[i];
	u = i;
      }
    }
     
    if(mincost == INF) break;
    
    color[u] = BLACK;
     
    for(v = 1;v <= n;v++){
      if(color[v] != BLACK && a[u][v] < d[v]){
	pi[v] = u;
	d[v] = a[u][v];
      }
    }
    color[v] = BLACK;
  }
 
  for(i = 1;i <= n; i++){
    if(pi[i] != -1) total += a[i][pi[i]];
  }
 
  return total;
}

 
int main()
{
  int i,j;
 
  scanf("%d",&n);
 
  for(i = 1;i <= n;i++){
    for(j = 1;j <= n;j++){
      scanf("%d",&a[i][j]);
      if(a[i][j] == -1) a[i][j] = INF;
    }
  }
 
   printf("%d\n",prim());
    
   return 0;
 
}