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 <stdio.h>
#include <iostream>
using namespace std;

#define NUM 100
#define BLACK 0
#define GREY 1
#define WHITE 2
#define NIL -1
#define INF 1000000000
int A[NUM][NUM];

int V[NUM];
int color[NUM];

void init(){
    for(int i = 0; i < NUM; i++){
        color[i] = WHITE;
        V[i] = INF;
    }

}

int main(void){
    init();

    int n;
    scanf("%d", &n);

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

    int next_node = 0;
    int sum = 0;
    while(1){
        color[next_node] = BLACK;
        for(int i = 0; i < n; i++){
            if(A[next_node][i] == NIL){
                continue;
            }
            V[i] = min(V[i], A[next_node][i]);
        }

        next_node = NIL;
        int min_dist = INF;
        for(int i = 0; i < n; i++){
            if(color[i] == BLACK){
                continue;
            }
            if(V[i] < min_dist){
                next_node = i;
                min_dist = V[i];
            }
        }
        if(min_dist == INF){
            break;
        }else{
            sum += min_dist;
        }
    }

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

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 (true) {
		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 <set>

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)

const int INF = 1 << 21;
const int SIZE = 101;
int a[SIZE][SIZE];

int prim(int n) {
  int d[n], p[n], state[n];

  rep(i, n) {
    d[i] = INF;
    p[i] = -1;
    state[i] = 0;
  }

  d[0] = 0;

  while (1) {
    int minv = INF, u = -1;

    rep(i, n) {
      if (d[i] < minv && state[i] != 1) {
        minv = d[i];
        u = i;
      }
    }

    if (u == -1) break;
    state[u] = 1;

    rep(i, n) {
      if (a[u][i] != INF && state[i] != 1) {
        if (d[i] > a[u][i]) {
          d[i] = a[u][i];
          p[i] = u;
        }
      }
    }
  }

  int sum = 0;
  rep(i, n) {
    if (p[i] != -1) { sum += a[i][p[i]]; }
  }

  return sum;
}

int main() {
  int n;
  std::cin >> n;

  rep(i, n) rep(j, n) {
    int m;
    std::cin >> m;
    if (m == -1) m = INF;
    a[i][j] = m;
  }

  std::cout << prim(n) << '\n';

  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <map>
#include <numeric>
#include <string>
#include <cmath>
#include <iomanip>
#include <queue>
#include <list>
#include <stack>
#include <cctype>
#include <cmath>

using namespace std;

/* typedef */

typedef long long ll;

/* constant */

const int INF = 1 << 30;
const int MAX = 100;
const int mod = 1000000007;
const double pi = 3.141592653589;

const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;

/* global variables */
vector< vector<int> > Adj(MAX, vector<int>(MAX, INF));
vector<int> color(MAX, WHITE);
vector<int> d(MAX, INF);
vector<int> p(MAX, -1);
int n;
int total_cost = 0;

/* function */
void prim();

/* main */
int main() {
    
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int a;
            cin >> a;
            if (a != -1)
                Adj[i][j] = a;
        }
    }

    prim();

    cout << total_cost << '\n';

}

void prim() {

    int u;
    int min_cost = INF;
    d[0] = 0;
    p[0] = -1;

    while (1) {

        u = -1;
        min_cost = INF;
        for (int i = 0; i < n; i++) {
            if (color[i] != BLACK && d[i] < min_cost) {
                u = i;
                min_cost = d[i];
            }
        }
        if (min_cost == INF) {
            break;
        }

        color[u] = BLACK;
        total_cost += min_cost;

        for (int v = 0; v < n; v++) {
            if (color[v] != BLACK && Adj[u][v] != INF) {
                // if (d[u] + Adj[u][v] < d[v]) {
                if (Adj[u][v] < d[v]) {
                    p[v] = u;
                    // d[v] = Adj[u][v] + d[u];
                    d[v] = Adj[u][v];
                    color[v] = GRAY;
                }
            }
        }
    }

}

C++: #include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define loop(i,a,b) for(i=a;i<b;i++)
#define rloop(i,a,b) for(i=a;i>=b;i--)
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
const int inf=1000000001;
const ll INF=1e16;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;
static const int N=100;

int n;
vii a(N,vi(N));

int prim();

int main(){
	int i,j;
	cin>>n;
	loop(i,0,n){
		loop(j,0,n){
			int k;
			cin>>k;
			a[i][j]=(k==-1)? inf:k;
		}
	}
	int m=prim();
	cout<<m<<endl;
}

int prim(){
	int u,minv,i;
	vi d(n,inf);
	vi p(n,-1);
	vi color(n,WHITE);
	d[0]=0;
	while(1){
		minv=inf;
		u=-1;
		loop(i,0,n){
			if(minv > d[i] && color[i]!=BLACK){
				u=i;
				minv=d[i];
			}
		}
		if(u==-1){
			break;
		}
		color[u]=BLACK;
		int v;
		loop(v,0,n){
			if(color[v]!=BLACK && a[u][v]!=inf){
				if(d[v]>a[u][v]){
					d[v]=a[u][v];
					p[v]=u;
					color[v]=GRAY;
				}
			}
		}
	}
	int sum=0;
	loop(i,0,n){
		if(p[i]!=-1){
			sum+=a[i][p[i]];
		}
	}
	return sum;
}