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>
using namespace std;
#define INF  (1<<21)
//int prim(int M[100][100], int n){
int M[100][100];
int prim(int n){
	int u, mincost;
	int color[n], d[n], p[n];
	for(int i=0; i<n; i++){
		color[i]=0;
		d[i]=INF;
		p[i]=-1;
	}
	d[0]=0;
	while(1){
		mincost=INF;
		u=-1;
		for(int i=0; i<n; i++){
			if(mincost>d[i] && color[i]!=2){
				u=i;
				mincost=d[i];
			}
		}
		if(u==-1)
			break;
		color[u]=2;
		for(int v=0; v<n; v++){
			if(color[v]!=2 && M[u][v]!=INF){
				if(d[v]>M[u][v]){
					d[v]=M[u][v];
					p[v]=u;
					color[v]=1;
				}
			}
		}
	}
	int sum=0;
	for(int i=0; i<n; i++)
		if(p[i]!=-1)
			sum+=M[i][p[i]];
	return sum;
}

int main(){
	int n;
	cin>>n;
	//int M[100][100];
	for(int i=0; i<n; i++){
		for(int j=0; j<n; j++){
			int e;
			cin>>e;
			if(e!=-1)
				M[i][j]=e;
			else
				M[i][j]=INF;
		}
	}
	cout<<prim(n)<<endl;
	return 0;
}

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

typedef pair<int, int> P;
const int M = 1000000007;

int prim_cost(vector<vector<P>> edge) {
    int n = edge.size();
    vector<int> vis(n, 0);
    int c = 0;
    priority_queue<P, vector<P>, greater<P>> q;
    q.push(P(0, 0));
    while (!q.empty()) {
        P p = q.top();
        q.pop();
        if (vis[p.second]) continue;
        vis[p.second] = 1;
        c += p.first;
        for (auto& e : edge[p.second]) {
            if (!vis[e.second]) {
                q.push(P(e.first, e.second));
            }
        }
    }
    return c;
}


int main() {
    int n;
    cin >> n;
    vector<vector<P>> edge(n);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int a;
            cin >> a;
            if (a != -1)
                edge[i].push_back(P(a, j));
        }
    }
    cout << prim_cost(edge) << "\n";
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#define wh 0
#define gr 1
#define bl 2
#define inf 2001
#define null (-1)
#define Max 100 
using namespace std;
int color[Max],m[Max][Max];
int d[Max],p[Max],n;
void prim(){
int i,j,u;
	for(i=0;i<n;i++){
	color[i]=wh;
		d[i]=inf;
	}
	d[0]=0;
	p[0]=-1;
	while(true){
	int mincost=inf;
		for(i=0;i<n;i++){
			if(color[i]!=bl && d[i]<mincost){
			mincost=d[i];
				u=i;
			}
		}
		if(mincost==inf)
		break;
		color[u]=bl;
		for(int v=0;v<n;v++){
			if(color[v]!=bl && m[u][v]!=null){
				if(m[u][v]<d[v]){
				d[v]=m[u][v];
					p[v]=u;
					color[v]=gr;
				}
			}
		}
	}
}

main(){
	int i,j;
	cin>>n;
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
	cin>>m[i][j];
			m[j][i]=m[i][j];
		}
	}
	prim();
	int ans=0;
	for(i=0;i<n;i++)
	ans+=d[i];
	cout<<ans<<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;

struct Node{
  int color, dist, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent;
    cout << " dist : " << node[i].dist << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0;
  node[p].dist = 0;

  while(true){
    //Printnodes();

    for(int i = 0; i < n; i++){
      if(M[p][i] >= 0 && node[i].color != BLACK){
        if(node[i].dist > M[p][i]){
          node[i].dist = M[p][i];
          node[i].parent = p;
          node[i].color = GRAY;
        }
      }
    }

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    //cout << "node " << p << " turns to BLACK!" << endl;
  }

  int sum = 0;
  for(int i = 0; i < n; i++){
    if(node[i].parent != -1)
      sum += M[i][node[i].parent];
  }
  cout << sum << endl;
  return 0;
}