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;

const int MAX = 100;

int count(bool check[MAX], int graph[MAX][MAX], int n,int i) {
	check[i] = true;
	int sum = 0;
	for (int j = 0; j < n; j++) {
		if (graph[i][j] != -1 && check[j] == false) {
			sum += count(check,graph, n, j);
			sum += graph[i][j];
		}
	}
	return sum;
}

int main() {
	int n;
	int g;
	int graph[MAX][MAX];

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

	//?§????
	for (int s = 0; s < n; s++) {
		//?????±???
		for (int m = 0; m < n; m++) {
			if (graph[s][m] == -1)continue;
			//??????
			for (int e = 0; e < n; e++) {
				if (graph[s][e] == -1 || graph[m][e] == -1)continue;
				if (graph[s][e] > graph[s][m] + graph[m][e]) {
					graph[s][e] = -1;
				}
			}
		}
	}

	bool check[MAX] = { false };
	cout << count(check, graph, n, 0) << endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
const int INF = 1e9 + 7;
const int MAX_V = 100;

int cost[MAX_V][MAX_V];
int mincost[MAX_V];
bool used[MAX_V];
int V;

int prim() {
    for (int i = 0; i < V; ++i) {
        mincost[i] = INF;
        used[i] = false;
    }

    mincost[0] = 0;
    int res = 0;

    while (true) {
        int v = -1;
        for (int u = 0; u < V; u++) {
            if (!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
        }

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

        for (int u = 0; u < V; u++) {
            if (cost[v][u] < mincost[u]) {
                mincost[u] = cost[v][u];
            }
        }
    }
    return res;
}

int main() {
    cin >> V;
    for (int i = 0; i < V; i++) {
        for (int j = 0; j < V; j++) {
            cin >> cost[i][j];
            if (cost[i][j] == -1) cost[i][j] = INF;
        }
    }
    cout << prim() << 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 <bits/stdc++.h>
using namespace std;
#define INF (1<<30)
#define MAX_N 100
typedef pair<int, int> P;

struct edge{
    int v[2], cost;
    edge(){}
    edge(int v0, int u0, int cost0){
        v[0] = v0; v[1] = u0; cost = cost0;
    }
    bool operator < (const edge &e) const {
        return cost > e.cost;
    }
};

int ans = 0, N;
vector<edge> E[MAX_N];

void prim(){
    bool seen[N];
    fill(seen, seen + N, false);
    priority_queue<edge> todo;
    seen[0] = true;
    for(int i = 0; i < E[0].size(); i++)
        todo.push(E[0][i]);
    while(!todo.empty()){
        edge e = todo.top(); todo.pop();
        if(seen[e.v[1]]) continue;
        ans += e.cost;
        seen[e.v[1]] = true;
        for(int i = 0; i < E[e.v[1]].size(); i++)
            if(!seen[E[e.v[1]][i].v[1]]) todo.push(E[e.v[1]][i]);
    }
}

int main(){
    cin >> N;
    for(int i = 0; i < N; i++)
        for(int j = 0; j < N; j++){
            int cost;
            cin >> cost;
            if(i < j && cost != -1){
                E[i].push_back(edge(i, j, cost));
                E[j].push_back(edge(j, i, cost));
            }
        }
    prim();
    cout << ans << endl;
    return 0;
}