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 MAX = 100;
static const int INFTY = (1<<21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int prim();

int n,M[MAX][MAX];

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;
}

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

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

struct Edge{
  int to,cost;
  bool operator<(const Edge&a)const{
    return cost>a.cost;
  }
};
struct Graph{
  Graph(int n):E(n),T(n),N(n){}
  vector<vector<Edge>>E,T;
  int N;
  void add_edge(int a,int b,int c){
    E[a].push_back({b,c});
    E[b].push_back({a,c});
  }
  void prim(int s){
    bool visited[N];
    priority_queue<pair<Edge,int>>Q;
    memset(visited,0,N);
    Q.push({{s,0},-1});
    while(!Q.empty()){
      Edge e=Q.top().first;
      int from=Q.top().second;Q.pop();
      if(visited[e.to])continue;
      visited[e.to]=1;
      if(from+1)T[from].push_back(e),T[e.to].push_back({from,e.cost});
      for(auto&a:E[e.to])
      if(!visited[a.to])Q.push({a,e.to});
    }
  }
  int get_cost(){
    int ret=0;
    for(auto&a:T)for(auto&b:a)ret+=b.cost;
    return ret/2;
  }
  vector<Edge>* get_MST(){
    return T.data();
  }
};

main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin>>N;
    Graph G(N);
    for(int i=0;i<N;++i)
        for(int j=0;j<N;++j){
            int a;
            cin>>a;
            if(~a) G.add_edge(i,j,a);
        }
    G.prim(0);
    cout<<G.get_cost()<<endl;
}

C++: #include <iostream>
#define MAX 100
#define INF (1<<21)
#define WHITE 0
#define GRAY 1
#define BLACK 2
using namespace std;

int M[MAX][MAX],n;
int prim(){
	int u,minv;
	int d[MAX],p[MAX],color[MAX];
	for(int i = 0;i < n;i++){
		d[i] = INF;
		p[i] = -1;
		color[i] = WHITE;
	}

	d[0] = 0;

	while(1){
		minv = INF;
		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] != INF){
				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(){
	int e;
	cin >> n;
	for(int i = 0;i < n;i++){
		for(int j = 0;j < n;j++){
			cin >> e;
			if(e == -1)M[i][j] = INF;
			else M[i][j] = e;
		}
	}

	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]]; //辺の重みの総和を計算
    }

    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;
}