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 <utility>
#include <string>
#include <algorithm>

using namespace std;


int P[10010]; // 0 ?????? 10000 ?????§????????????????????±?????????
void init(int N) { // ????????? ??????????????¨???????????????????????????
  for (int i=0; i<=N; ++i) P[i] = i;
  // ??¨: ????????? [0,N-1] ????????? [1,N] ?????????????????????
  // ???????????§???????????§???????????????????????§??? [0,N] ???????????¨??????
}
int root(int a) { // a ??? root(??£??¨???) ????±???????
  if (P[a] == a) return a; // a ??? root
  return (P[a] = root(P[a])); // a ????????? root ????±???????a ????????¨??????
}
bool is_same_set(int a, int b) { // a ??¨ b ???????????°?????????????±???????????
  return root(a) == root(b);
}
void unite(int a, int b) { // a ??¨ b ???????????°?????????????????¨??????
  P[root(a)] = root(b);
}


int N=0;
int A[100+10][100+10] = {0};

int cost[10100] = {0};
int src[10100] = {0};
int dst[10100] = {0};

pair<int,int> c_n[10100];



int main() {
  cin >> N;
  init(N+10);
  
  int k=0;
  for(int j=0;j<N;++j){
    for(int i=0;i<N;++i){
      cin >> A[i][j];
      //cout << A[i][j] << "|";
      if (A[i][j] != -1){
	cost[k] = A[i][j];
	src[k] = i;
	dst[k] = j;
	c_n[k] = make_pair(cost[k],k);
	++k;
      }
    }
    //cout << endl;
  }


  sort(c_n, c_n+k);

  

  int num = 0;
  int sum = 0;
  for(int i=0;i<k;++i){
    num = c_n[i].second;
    if(is_same_set(src[num], dst[num]) == 0){
      unite(src[num], dst[num]);
      sum += cost[num];
      //cout << num << " " << sum << endl;
    }
  }
  cout << sum << endl;
}

C++: #include<string.h>
#include<iostream>
#include<algorithm>
using namespace std;
#define ROOP1(i,n) for(int i=0;i<n;i++)
#define ROOP2(j,n) for(int j=0;j<n;j++)
#define Psi pair<string,int>
#define Pis pair<int,string>
#define Pii pair<int,int>
static const int INFTY = (1 << 21);
static const int MAX = 100;
static const int WHITE = 1;
static const int GRAY = 2;
static const int BLACK = 3;
// ??????????????????memset(a,0,sizeof(a));
// ?´???°?????? if(x<2)return0;else if(x==2)return1;if(x%2==0)return0;for(i=3;i*i<=x;i+=2){if(x%i==0)return0;}return1;}p440
//vector size();push_back(x);pop_back();begin();end();insert(p,x);erase(p);clear();
//stack  size();top();pop();push(x);emtpy();
//queue  size();front();pop();push(x);empty();
int n;
int M[MAX][MAX];
int color[MAX], d[MAX], p[MAX];

int main(){
	cin >> n;
	ROOP1(i, n){
		ROOP2(j, n){
			cin >> M[i][j];
		}
	}
	for (int i = 0; i < n; i++){
		d[i] = INFTY;
		color[i] = WHITE;
		p[i] = -1;
  	}
	bool flag =  true;
	d[0] = 0;
	while (flag){
		int mincost = INFTY; int u = 0;
		for (int i = 0; i < n; i++){
			if (color[i] != BLACK && d[i] < mincost){
				mincost = d[i];
				u = i;
			}
		}
		if (mincost == INFTY) break;
		color[u] = BLACK;
		for (int v = 0; v < n; v++){
			if (M[u][v] != -1 && color[v] != BLACK){
				if (d[v] > M[u][v]){
					d[v] = M[u][v];
					p[v] = u;
					color[v] = GRAY;
				}
			}
		}
 	}
	int sum = 0;
	for (int i = 0; i < n; i++){
		sum += M[i][p[i]];
	}
	cout << sum << endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, M[MAX][MAX];

int prim() {
	int u, minv;
	int d[MAX], p[MAX], color[MAX];
	for (int i = 0; i < n; i++)
	{
		d[i] = INFTY;
		p[i] = -1;
		color[i] = WHITE;
	}
	d[0] = 0;
	while (1)
	{
		minv = INFTY;
		u = -1;
		for (int i = 0; i < n; i++)
		{
			if (minv > d[i] && color[i] != BLACK) {
				u = i;
				minv = d[i];
			}
		}
		if (u == -1) break;
		color[u] = BLACK;
		for (int v = 0; v < n; v++)
		{
			if (d[v] > M[u][v]) {
				d[v] = M[u][v];
				p[v] = u;
				color[v] = GRAY;
			}
		}
		int sum = 0;
		for (int i = 0; i < n; i++)
		{
			if (p[i] != -1) sum += M[i][p[i]];
		}
	}
		return sum;
	}

	int main() {
		cin >> n;

		for (int i = 0; i < n; i++)
		{
			for (int j = 0; j < n; j++) {
				int e; cin >> e;
				M[i][j] = (e == -1) ? INFTY : e;
			}
		}
		cout << prim() << endl;
		return 0;
	}

C++: #include<iostream>

using namespace std;

#define WHITE 0
#define BLACK 2
#define GRAY 1
#define MAX 100
#define INFITY 1<<21

int n,M[MAX][MAX];

int prim()
{
	int d[MAX],color[MAX],p[MAX];

	for (int i = 0; i < n; ++i)
	{
		d[i]=INFITY;
		p[i]=-1;
		color[i]=WHITE;
	}

	d[0]=0;
	color[0]=GRAY;
	while(1){
		int u=-1;
		int minv=INFITY;
		// 把距离最小的顶点加入MST
		for (int i = 0; i < n; ++i)
		{
			if (minv>d[i]&&color[i]==GRAY)
			{
				minv=d[i];
				u=i;
			}
		}
		if (u==-1)
		{
			break;
		}
		color[u]=BLACK;

		// 更新距离
		for (int i = 0; i < n; ++i)
		{
			if (color[i]!=BLACK&&d[i]>M[u][i])
			{
				d[i]=M[u][i];
				color[i]=GRAY;
				p[i]=u;
			}
		}
	}
	int sum=0;
	for (int i = 0; i < n; ++i)
	{
		if (p[i]!=-1)
		{
			sum+=M[i][p[i]];
		}
	}

	return sum;
}

int main(int argc, char const *argv[])
{
	cin>>n;
	for (int i = 0; i < n; ++i)
	{
		for (int j = 0; j < n; ++j)
		{
			int v;
			cin>>v;
			M[i][j]=(v==-1)?INFITY:v;
		}
	}
	cout<<prim()<<endl;
	return 0;
}