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>
#define MAX 150
#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++;
      }
    }
  }
  // cout << endl;
  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) {
    // if (edge[i].first == -1) continue;
    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;
      // if (ra != a && rb == b){     
      //   V[b] = ra;
      // } else if (ra == a && rb != b) {
      //   V[a] = rb;
      // } else if (ra == a && rb == b) {        
      //   V[a] = b;
      // } else if (ra != a && rb != b) {                
      //   V[ra] = rb;
      // }
    }
  }
  cout << sum << endl;
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i,n) for(ll i=0; i<(n); i++)
#define REP2(i,x,n) for(ll i=x; i<(n); i++)
#define REP3(i,x,n) for(ll i=x; i>(n); i--)
#define ALL(n) begin(n),end(n)

#define SENTINEL 2000000000
#define NIL -1
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
const long long INF = numeric_limits<long long>::max();
static const int MAX = 100;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;
static const int INFTY = (1<<21);

int n,M[MAX][MAX];

//primのアルゴリズム
int prim(){
    int color[MAX],d[MAX],p[MAX];
    int minv;
    for (int u = 0; u < n; u++)
    {
        color[u] = WHITE;
        d[u] = INFTY;
        p[u] = -1;
    }
    d[0]=0; 
    while(1){
        minv = INFTY;
        int u= -1;
        for (int i = 0; i < n; i++)
        {
            if(color[i]!=BLACK&&d[i]<minv){
                minv = d[i];
                u = i;
            }
        }
        if (u == -1)break;
        color[u] = BLACK;
        for (int v = 0; v < n; v++)
        {
            if(color[v]!=BLACK&&M[u][v]!=INFTY){
                if(M[u][v]<d[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;
    REP(i,n){REP(j,n){
        int e;
        cin >> e;
        M[i][j] = (e ==-1)?INFTY:e;    
        }
    }
    cout << prim() << endl;

    return 0;
}

C++: #include <iostream>
using namespace std;
 
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INFTY 1000000
 
 
int n,M[100][100],color[100],d[100],p[100];
 
//プリム法
int prim(){
  int i,u;

  //初期化
  for( i = 0; i < 100; i++ ){ 
    color[i] = WHITE;
    d[i] = INFTY;
    p[i] = -1;   
  }
  
  d[0] = 0;
  
  
  while(1){
    u = -1;
    int mincost = INFTY;
     
    for( i = 0; i < n; i++ ){
      if( color[i] != BLACK && d[i] < mincost ){
    mincost = d[i];
    u = i;
      }
    }
    
    if( u == -1 ) break;
 
    color[u] = BLACK;
 
    //最小全域木の更新
    for( int v = 0; v < n; v++ ){
      if( color[v] != BLACK && M[u][v] != INFTY ){
    if( M[u][v] < d[v] ){
      d[v] = M[u][v];
      p[v] = u;
      color[v] = GRAY;
    }
      }
    }
  }
  //最小全域木の辺の重みの総和をもとめる
  int sum = 0;
  for( i = 0; i < n; i++ ){
    if( p[i] != -1 ) sum+= M[i][p[i]];
  }
  return sum;
}
 
int main(){
  //入力
  cin >> n;
  for( int i = 0; i < n; i++ ){
    for( int j = 0; j < n; j++ ){
      cin >> M[i][j];
      if( M[i][j] == -1 ) M[i][j] = INFTY;
    }
  }
 
  cout << prim() << endl;
 
  return 0;
}