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 <stdio.h>
#include <iostream>
#include <algorithm>
using namespace std;

#define N 100

void searchIndex(int mat[][N], int n, int obj, int *row, int *col);
void changeGroup(int group[], int n, int g_old, int g_new);

int main(void)
{
	int n;
	cin >> n;

	int group[N];
	for (int i = 0; i < n; i++) group[i] = i;

	int a[N][N];	
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int aij;
			cin >> aij;
			a[i][j] = aij;
		}
	}

	int e[N * N];
	int k = 0;
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			e[k++] = a[i][j];
		}
	}

	sort(e, e + k);

	int p = 0;
	while (e[p] == -1) p++;

	int cnt = 0;
	for (int q = p; q < k; q++) {
		int i, j;
		searchIndex(a, n, e[q], &i, &j);
		if (group[i] == group[j]) continue;
		cnt += e[q];
		if (group[i] > group[j]) changeGroup(group, n, group[i], group[j]);
		else changeGroup(group, n, group[j], group[i]);
	}

	cout << cnt << endl;

	return 0;
}

void searchIndex(int mat[][N], int n, int obj, int *row, int *col)
{
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			if (mat[i][j] == obj) {
				mat[i][j] = -1;
				*row = i;
				*col = j;
				return;
			}
		}
	}
}

void changeGroup(int group[], int n, int g_old, int g_new)
{
	for (int i = 0; i < n; i++) {
		if (group[i] == g_old) group[i] = g_new;
	}
}

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;
		minv = d[i];
		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<bits/stdc++.h>
using namespace std;

int main(){
  int n;
  int a[100][100],b[100]={},c[100]={};
  c[0]=1;
  cin>>n;
  for(int i=0;i<n;i++)
   for(int j=0;j<n;j++)cin>>a[i][j];

  int k=1,min=10000,min1=0,ans=0;
  while(1){
   for(int i=0;i<k;i++)
    for(int j=0;j<n;j++)
     if(a[b[i]][j]<min && a[b[i]][j]!=-1 &&c[j]!=1){
      min=a[b[i]][j];
      min1=j;
    }
   if(k==n)break;
   b[k]=min1;
   c[min1]=1
   ans+=min;
   k++;
  }

 cout<<ans<<endl;
 return 0;
}

C++: #include <iostream>
#include <vector>
#include <climits>

using namespace std;

const int kSize = 100001;

vector<int> V;

struct Node {
    int to;
    int weight;

    Node(int _to, int _weight) {
        to = _to;
        weight = _weight;
    }
};

int n;
vector<Node> adj[kSize];
bool isMarked[kSize];
int tree[kSize];
int ans = 0;

pair<int,int> GetMinWeight(int v) {
    int ans = INT_MAX;
    int vertex = -1;
    for (int i = 0; i < adj[v].size(); ++i) {
        int u = adj[v][i].to;
        if (!isMarked[u]) {
            //ans = min(ans, adj[v][i].weight);
            //vertex = u;
            if (adj[v][i].weight <= ans) {
                ans = adj[v][i].weight;
                vertex = u;
            }
        }
    }

    ans = ans == INT_MAX ? -1 : ans;
    return make_pair(ans, vertex);
}

int GetMinVertex() {
    int v = -1;
    int min = INT_MAX;
    for (int i = 0; i < V.size(); ++i) {
        pair<int, int> p = GetMinWeight(V[i]);
        int weight = p.first;
        if (weight != -1 && weight <= min) {
            min = weight;
            v = p.second;
        }
    }

    ans += min;
    return v;
}

int Prime() {
    V.push_back(1);
    isMarked[1] = true;

    while (V.size() < n) {
        int v = GetMinVertex();
        //cout << v << endl;
        V.push_back(v);
        isMarked[v] = true;
    }
}

int main() {
    fill(isMarked, isMarked + kSize, false);
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            int weight;
            cin >> weight;
            if (weight != -1) {
                adj[i].emplace_back(j, weight);
            }
        }
    }

    Prime();
    cout << ans << endl;
}