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>
#include <utility>
#include <algorithm>
using namespace std;

int m,n,x,ans;
int P[100+10],edge1[2000+10],edge2[2000+10];


int root(int a){
	if (P[a] == a) return a;
	return (P[a] = root(P[a]));
}

bool same(int a, int b){
	return root(a)==root(b);
}
	
void unite(int a, int b){
	P[root(a)] = root(b);
}

int main() {
	pair<int,int> edges[2000+10];
	cin >> n;
	
	for (int i=1; i<=n; i++){
		P[i] = i;
	}
	
	m = 0;
	for (int i=1; i<=n; i++){
		for (int j=1; j<=n; j++){
			cin >> x;
			if (x>-1){
				edge1[m] = i;
				edge2[m] = j;
				edges[m] = make_pair(x, m);
				m+=1;
			}
		}
	}
	
	sort(edges, edges+m);
	n=1;
	for (int i=0; i<m; i++){
		if (n>=m) break;
		if (!same(edge1[edges[i].second], edge2[edges[i].second])){
			unite(edge1[edges[i].second], edge2[edges[i].second]);
			ans += edges[i].first;
			n+=1;
		}
	}
	
	cout << ans << endl;
	
}

C++: #if 0
????????£????????????1.5h
??¢?????????????????§??????????????¢??°????????£????????????sum????¨??????¨????????????????????£????????§?????????
???????????¢??????????????§????????????????????????????????????"-1"???????????????????????????????????§???????????§????????¨???????°???????????????????
#endif

#include <iostream>
#include <algorithm>
#include <utility>
using namespace std;

int P[10000+10];

void init(int N){
	for(int i=0;i<=N;++i) P[i]=i;
}
int root(int a){
	if(P[a]==a)return a;
	else return(P[a]=root(P[a]));
}
bool is_same_set(int a,int b){
	return root(a)==root(b);
}
void unite(int a,int b){
	P[root(a)]=root(b);
}
int main(){
	int N;
	cin>>N;
	int A[N][N];
	
	for(int i=0; i<N;i++){
		for(int j=0;j<N;j++){
			cin>>A[j][i]; //???????????\???
		}
	}

	int M = 0; 
	int cost[N*N],src[N*N],dst[N*N];
	for (int r=0; r<N;r++)
		for (int c=0; c<r;c++) //r<c???????§?????????????
			if (A[r][c] > -1) {
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				M += 1;
			}
	pair<int,int> edges[2000+100];
	for(int i=0;i<M;i++)
		edges[i]=make_pair(cost[i],i); //first???????????????second???ID
	sort(edges,edges+M);
	
	//for(int i=0;i<M;++i)
		//cout<<edges[i].first<<endl;

	init(N);
	int sum=0;
	for(int i=0;i<M;i++){
		if(is_same_set(src[edges[i].second],dst[edges[i].second])==0){
			unite(src[edges[i].second],dst[edges[i].second]);
			sum+=edges[i].first;
		}
	}
		cout<<sum<<endl;
}

C++: #include<iostream>
using namespace std;
#define INFTY (1 << 30)

enum Color {
	WHITE,
	GRAY,
	BLACK,
};

void Prim(int verValWeight[][100], int verNum) {
	int distance[100];
	Color color[100];
	int parent[100];
	for (int i = 0; i < verNum; i++)
		color[i] = WHITE;
	distance[0] = 0;
	parent[0] = -1;

	while (true) {
		int min_cost = INFTY;
		int subScript;
		for (int i = 0; i < verNum; i++) {
			if (color[i] != BLACK && distance[i] < min_cost) {
				min_cost = distance[i];
				subScript = i;
			}

			if (min_cost == INFTY) break; //end

			color[subScript] = BLACK;

			for (int i = 0; i < verNum; i++) {
				if (color[i] != BLACK && verValWeight[subScript][i] != INFTY) {
					if (verValWeight[subScript][i] < distance[i]) {
						distance[i] = verValWeight[subScript][i];
						parent[i] = subScript;
						color[i] = GRAY;
					}
				}
			}
		}
	}

	int weight_sum = 0;
	for (int i = 0; i < verNum; i++)
		if (parent[i] == -1)
			weight_sum += verValWeight[i][parent[i]];
	cout << weight_sum << endl;

}

int main() {
	int verNum;
	int verValWeight[100][100];
	int parent[100];

	cin >> verNum;
	for (int i = 0; i < verNum; i++)
		for (int j = 0; j < verNum; j++) {
			cin >> verValWeight[i][j];
			if (verValWeight[i][j] == -1) verValWeight[i][j] = INFTY;
		}

	Prim(verValWeight, verNum);

	return 0;
}

C++: #include <stdio.h>

#define MAX 101
#define INF 100000

int main(){
  int i,j,n,min,k=1,minNode,sum=0;
  int a[MAX][MAX],x{[MAX],g[MAX];

  scanf("%d",&n);
  for(i=0 ; i<n ; i++){
    for(j=0 ; j<n ; j++){
      scanf("%d",&a[i][j]);
    }
  }


  x[0] = 0;
  g[0] = 1;
  for(i=1 ; i<n ; i++){
    g[i] = 0;
  }
  
  while(1){
    min = INF;
    
    for(i=0 ; i<k ; i++){
      for(j=0 ; j<n ; j++){
	if(min > a[x[i]][j] && a[x[i]][j]!= -1 && g[j] != 1){
	  min = a[x[i]][j];
	  minNode = j;
	}
      }
    }

    if(k!=n){
      x[k] = minNode;
      g[minNode] = 1;
      k++;
      sum += min;
    }
    else{ 
      break; 
    }
    
  }

  printf("%d\n",sum);
  
  return 0;
}