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 <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 2100

int main() {
  int n; cin >> n;
  vector<vector<int>> G(n, vector<int>(n));
  rep(i, n)rep(j, n) cin >> G.at(i).at(j);

  vector<int> color(n); vector<int> mindis(n);
  rep(i, n) mindis.at(i) = INF;
  vector<int> par(n);
  int ans = 0;
  mindis.at(0) = 0;
  color.at(0) = GRAY;
  par.at(0) = -1;

  while (true) {
    int m = INF;
    int now = 0;
    rep(i, n) {
      if (color.at(i) == GRAY && mindis.at(i) < m) {
        m = mindis.at(i);
        now = i;
      }
    }

    if (m == INF) break;

    color.at(now) = BLACK;
    if (par.at(now) != -1) {
      ans += G.at(par.at(now)).at(now);
    }

    rep(i, n) {
      if (G.at(now).at(i) < mindis.at(i) && G.at(now).at(i) != -1 && color.at(i) != BLACK) {
        mindis.at(i) = G.at(now).at(i);
        color.at(i) = GRAY;
        par.at(i) = now;
      }
    }
  }
  cout << ans << endl;
}

C++: #include <iostream>
#include <vector>
using namespace std;

const int INF = 1000000000;

int main() {
    int n;
    cin >> n;
    vector< vector<int> > cost(n, vector<int>(n, INF));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int a;
            cin >> a;
            cost[i][j] = (a == -1) ? INF : a;
        }
    }

    vector<int> mincost(n, INF);
    vector<bool> used(n, false);
    mincost[0] = 0;

    int res = 0;
    while (true) {
        int v = -1;
        for (int u = 0; u < n; 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 < n; u++) {
            mincost[u] = min(mincost[u], cost[u][v]);
        }
    }

    cout << res << endl;
    return 0;
}

C++: #include <iostream>
#include <utility>
#include <algorithm>
#define MAX 3000
#define rep(i,p) for(int i=0;i<p;i++)
#define rep1(i,p) for(int i=1;i<=p;i++)
using namespace std;
int n,temp,a,b,size,ra,rb;
int A[MAX];
int B[MAX];
int W[MAX];
int V[MAX];
pair<int,int> edge[MAX];
int root (int child) {
  int a = child;
  while (V[a] != a) {
    a = V[a];
  }
  return a;
}
int main(){
  size = 0;
  cin >> n;
  rep(i,n) {
    rep(j,n) {
      cin >> W[size];
      if (i <= j && W[size] != -1) { 
        A[size] = i;
        B[size] = j;        
        edge[size].first = W[size];
        edge[size].second = size;
        size++;
      }
    }
  }
  // rep(i,size) {
  //   cout << A[edge[i].second] << " " << B[edge[i].second]
  //        << " " << edge[i].first << endl;;
  // }
  // sort by lenght of edge
  sort(edge, edge+size);
  
  int sum = 0;
  rep(i,n) V[i] = i;
  rep(i,size) {
    temp = edge[i].second;
    // a , b : vertex
    a = A[temp];
    b = B[temp];
    ra = root(a);
    rb = root(b);
    if (ra != rb) {
      // ?????????????????????
      sum += edge[i].first;
      V[ra] = rb;
    }
  }
  cout << sum << endl;
  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int MAX=100;
static const int INF=(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,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(){
  cin >> n;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int e; cin >> e;
      if(e==-1)M[i][j]=INF;
      else M[i][j]=e;
    }
  }
  cout << prim() << endl;
}