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;
static const int INFTY = (1 << 21);
int n,M[100][100];

int prim(){
  int u,v,d[100],p[100],color[100],mincost;
  for (int i = 0; i < n; i++) {
    color[i] = 0;
    d[i] = INFTY;
    p[i] = -1;
  }
  d[0] = 0;

  while (1) {
    mincost = INFTY;
    u = -1;
    for (int i = 0; i < n; i++) {
      if (color[i] != 2 && d[i] < mincost) {
        u = i;
        mincost = d[i];
      }
    }
    if (u == -1) break;
    color[u] = 2;
    for (v = 0; v < n; v++) {
      if (color[v] != 2 && M[u][v] != INFTY) {
        if (M[u][v] < d[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 t;
  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<bits/stdc++.h>
using namespace std;
int main(){
	int mapp[101][101];
	int d[101],vis[101];
	int ans=0,n,u;
	cin>>n;
	for (int i=0; i<n; i++)
	    for (int j=0; j<n; j++)
	        cin>>mapp[i][j];
	memset(vis,0,sizeof(vis));
	memset(d,0x1f1f1f1f,sizeof(d));
	d[0]=0; 
	while (true){
		  int minn=0x1f1f1f1f;
		  for (int i=0; i<n; i++)
		  	  if (!vis[i] && d[i]<minn){
		  	  	 minn=d[i]; u=i;
			  }
		  vis[u]=1;
		  if (minn==0x1f1f1f1f)
		     break;
		  for (int i=0; i<n; i++)
		      if (!vis[i] && mapp[u][i]!=-1 && mapp[u][i]<d[i]){
		      	 d[i]=mapp[u][i];
			  }
	}
	for (int 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;

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(color[v] != BLACK && M[u][v] != INFTY){
                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 <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <cctype>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <numeric>
#include <complex>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <iostream>
#include <iterator>
#include <algorithm>
using namespace std;
using ll = long long;
using VL=vector<ll>;

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
const long long INF =  999999999;

typedef pair<int,int> P;

int cost[2010][2010];
int mincost[2020];
bool used[2020];
int V;

int main(){
  int n,res=0;
  cin>>n;
  REP(i,n){
    REP(j,n){
      cin>>cost[i][j];
    }
  }
  REP(i,n){
    mincost[i]=INF;
    used[i]=false;
  }
  mincost[0]=0;

  while(true){
    int v=-1;

    REP(u,n){
      if(!used[u] &&(v==-1 || mincost[u]<mincost[v]))v=u;
    }

    if(v==-1)break;
    used[v]=true;
    res += mincost[v];

    REP(u,n){
      if(cost[v][u]==-1)continue;
      mincost[u]=min(mincost[u],cost[v][u]);
    }
  }
  cout<<res<<endl;

}