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 <cstdio>
using namespace std;

static const int MAX = 100;
static const int INFTY = ( 1 << 21 );
static const int WHITE = 1;
static const int GLAY  = 2;
static const int BLACK = 3;

int M[MAX][MAX];
int d[MAX], p[MAX], color[MAX];

// ??????????????¢?????´?????????
int prim( int n )
{

	int mincost, u, msum = 0;

	// color?????????WHITE(????¨????)???d??????(????°??????????????¨????????????????)???INFTY???p??????(????°???¨?????¨?§????????¬????????£???¨?????????????????????????¨???¶????????????)???-1??§?????????????????????
	for( int i = 0; i < n; i++ ) { color[i] = WHITE; d[i] = INFTY; p[i] = -1; }

	// ????????????????¨?????????????????????????????????????????´????0(????????????)
	d[0] = 0;

	while( 1 ) {

		mincost = INFTY;	// ????°?????????????INFTY??§?????????
		u		= -1;		// ??????????£????????????????-1??§?????????(????¨??????¨????????????)

		// d???????????°??????????¨??????????????°????????????????????°?????????£?????´??????????°?????????????d[i]?????????????£????????????????i(?????¶???????°??????????????????????)??¨??????
		for( int i = 0; i < n; i++ ) {
			if( color[i] != BLACK && d[i] < mincost ) { mincost = d[i]; u = i; }
		}

		// ??????????£????????????????-1(????????\????????¢?´¢????????????)?????¨???while??????break
		if( u == -1 ) break;

		// ??????????£???°????¨????????????¨??????
		color[u] = BLACK;

		// ????????°?????°???
		for( int v = 0; v < n; v++ ) {

			// ?????¨??°?????????????¨????????????§????????????????????°????????????????????¨??????(INFTY??§?????????)??¨???
			if( color[v] != BLACK && M[u][v] != INFTY ) {
				// ???????????????????°????????????????????°???????????????§?????£?????¨???
				if( M[u][v] < d[v] ) {

					d[v]	 = M[u][v];		// ????°????????????????????????????
					p[v]	 = u;			// ????°?????£???°?????????????°???°(????????????)?????????
					color[v] = GLAY;		// ?¨??????¶??????MST????±???????????????¨??????

				}
			}

		}

	}

	for( int i = 0; i < n; i++ ) {
		if( p[i] != -1 ) msum += M[i][p[i]];	// ???????????????-1(?????¨??????????°???¨?????¨????????????)??§?????£?????´????????°????????????????????????????¶?????????????
	}

	return msum;	// ????°???¨?????¨?????¨??????????????????????????¨??????

}

int main()
{

	int n, a;

	// ????????°
	scanf( "%d", &n );

	for( int i = 0; i < n; i++ ) {
		for( int j = 0; j < n; j++ ) {

			// ??£??\?????????????´??????\???
			// -1?????\??????????????´?????????????????????(INFTY??£??\)
			scanf( "%d", &a );
			M[i][j] = ( a == -1 ) ? INFTY : a;
		
		}
	}

	// prim??¢??°???????????????printf
	printf( "%d\n", prim( n ) );

	return 0;
}

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

void init(int n, vector<int>& v){
  v.resize(n);
  for(int i = 0; i < n; i++){
    v[i] = i;
  }
}

int root(int a, vector<int>& v){
  if(v[a] == a) return a;
  return (v[a] = root(v[a], v));
}

bool same(int a, int b, vector<int>& v){
  return root(a,v) == root(b,v);
}

void unite(int a, int b, vector<int>& v){
  v[root(a,v)] = root(b,v);
}


int main(){
  int n;
  cin >> n;
  vector<vector<int> > a(n, vector<int>(n, -1));
  for(int i = 0; i < n; i++)
    for(int j = 0; j < n; j++)
      cin >> a[i][j];

  vector<int> cost, src, dst;
  for(int i = 0; i < n; i++){
    for(int j = i+1; j < n; j++){
      if(a[i][j] > -1){
        cost.push_back(a[i][j]);
        src.push_back(i);
        dst.push_back(j);
      }
    }
  }
  vector<pair<int, int> > edges(cost.size());

  for(int i = 0; i < cost.size(); i++){
    // cout << "cost" << cost[i] << endl;
    // cout << "i" << i << endl;
    edges[i] = make_pair(cost[i], i);
    // cout << edges[i].first << " : " << edges[i].second << endl;
  }

  sort(edges.begin(),edges.end());

  for(int i = 0; i < cost.size(); i++)
    cout << edges[i].first << " : " << edges[i].second << endl;

  int sum = 0;
  vector<int> units;
  init(n, units);
  for(int i = 0; i < edges.size(); i++){
    int idx = edges[i].second;
    int s = src[idx], d = dst[idx];
    // cout << s << "," << d << endl;
    if(same(s, d, units))
      continue;
    unite(s, d, units);

    sum += cost[idx];
  }

  cout << sum << endl;
}