Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

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 <iostream>
#include <stdio.h>
#include <vector>

#define inf 2001
using namespace std;

int main() {
	int n, tmp;
	int g[100][100];//与えられるグラフ
	bool used[100] = {}; //訪問済みを１、未訪問を０とする
	used[0] = 1;
	cin >> n;
	vector <int> x;

	//入力を受け取る
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			cin >> tmp;
			g[i][j] = tmp;
		}
	}
	x.push_back(0);
	int s, t, min, minn;
	int d[100] = {};
	while (x.size() != n) {
		min = inf;
		for (int i = 0; i < x.size(); ++i) {
			for (int j = 0; j < n; ++j) {
				if (!used[j] && g[x[i]][j] < min && g[x[i]][j] != -1) {//未訪問　かつ　最小値かつ　つながっている
					s = x[i];
					t = j;
					min = g[s][t];
				}
			}
		}
		x.push_back(t);
		used[t] = 1;
		d[t] = g[s][t];
	}
	int sum = 0;
	for (int i = 0; i < n; ++i) {
		sum += d[i];
	}
	cout << sum << endl;
}

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

int main(void)
{
	int n, now = 0, flag[101] = {};
	long ans = 0, an[100][100], min[100];

	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++)
			cin >> an[i][j];
		min[i] = 1000000000;
	}

	do {
		long key = LONG_MAX, key_i;
		flag[now] = 1;
		flag[100] = 0;

		for (int i = 0; i < n; i++) {
			if (an[now][i] != -1 && an[now][i] < min[i] && flag[i] == 0)
				min[i] = an[now][i];
			if (flag[i] == 0 && min[i] < key) {
				key = min[i];
				key_i = i;
			}
			if (flag[i] == 1)
				flag[100]++;
		}

		now = key_i;
		ans += key;

	} while (flag[100] != n - 1);

	cout << ans << endl;

	return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(1){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

  for ( i = 0; i < n; i++ ){
    if ( p[i] != -1 ) sum += M[i][p[i]];
  }

  printf("%d\n", sum);

  return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <set>
#include <vector>
#define FOR(i,k,n) for (int (i)=(k); (i)<(n); ++(i))
#define REP(i,n) FOR(i,0,n)
#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define all(v) begin(v), end(v)
using namespace std;
typedef pair<int,int> PII;

int P[100]; //union_find

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

bool same(int x, int y){
    return root(P[x]) == root(P[y]);
}

void unite(int x, int y){
    P[root(x)] = root(y);
}

int main(){
    int n;
    cin >> n;
    int g[n][n];
    vector<pair<int,PII>> V;
    REP(i,n){
        REP(j,n){
            cin >> g[i][j];
            if(i<j && g[i][j] >= 0) V.pb(mp(g[i][j],mp(i,j)));
        }
    }
    sort(all(V));
    REP(i,n){
        P[i] = i;
    }
    int wsum = 0, count = 0;
    REP(i,n*n){
        int x = V[i].snd.fst;
        int y = V[i].snd.snd;
        if(same(x,y)) continue;
        unite(x,y);
        wsum += V[i].fst;
        count++;
        if(count == n-1) break;
    }

    cout <<wsum<<endl;

    return 0;
}

C++: #ifdef LOCAL_BUILD
#include "pch.h"
#define DLOG(msg) cout << "#" << __LINE__ << ":" << msg << endl;
#define DLOG_V(var) \
  cout << "#" << __LINE__ << ":" << #var << " : " << var << endl;
#else
#include <bits/stdc++.h>
#define DLOG(msg)
#define DLOG_V(var)
#endif
using namespace std;

struct Edge {
  int weight;
  int source;
  int destination;
};

int main() {
  int n;
  cin >> n;
  auto cmp = [](const Edge& lhs, const Edge& rhs) {
    return lhs.weight > rhs.weight;
  };
  vector<vector<Edge>> edges(n, vector<Edge>());
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      int w;
      cin >> w;
      if (w != -1) {
        Edge e {w, i, j};
        edges[i].push_back(move(e));
      }
    }
  }

  int total_weight = 0;
  unordered_set<int> contained;
  contained.insert(0);
  priority_queue<Edge, vector<Edge>, decltype(cmp)> q(cmp);
  for (auto&& e : edges[0]) {
    q.push(e);
  }
  while (static_cast<int>(contained.size()) < n) {
    auto e = q.top();
    q.pop();
    if (contained.find(e.destination) == contained.end()) {
      total_weight += e.weight;
      contained.insert(e.destination);
      for (auto&& edge : edges[e.destination]) {
        q.push(edge);
      }
    }
  }
  cout << total_weight << endl;
}