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];  // dは重みが最小の辺の重み，pはMSTにおける頂点の親を，colorは訪問状態を記録

    for (int i = 0; i < n; i++) {
        d[i] = INFTY;      // 重みは十分に大きい数で初期化
        p[i] = -1;         // 親を初期化
        color[i] = WHITE;  // 訪問してないということで初期化
    }

    d[0] = 0;

    while (1) {
        minv = INFTY;
        u = -1;  // 最小の重みを持つ頂点
        for (int i = 0; i < n; i++) {
            if (minv > d[i] && color[i] != BLACK) {  // d[i]が最小の重みより小さく，iをまだ通ったことがなければ
                u = i;        // 頂点を更新する
                minv = d[i];  // 最小値を更新する
            }
        }
        if (u == -1) {  // 最小値が更新されないときは終了
            break;
        }
        color[u] = BLACK;  // 最小値を持つ頂点を訪問済みにする
        for (int v = 0; v < n; v++) {
            if (color[v] != BLACK & M[u][v] != INFTY) {  // vが訪問済みでなく，uからvに行く重みが更新されているとき
                if (d[v] > M[u][v]) {  // vの最小の重みがuからvへ行くときの重みより大きい時
                    d[v] = M[u][v];  // 最初の重みを更新
                    p[v] = u;  // 頂点の親を変更する
                    color[v] = GRAY;  // vを通ったことにする
                }
            }
        }
    }
    int sum = 0;
    for (int i = 0; i < n; i++) {
        if (p[i] != -1) {  // MSTにおける頂点の親が-1でなけれが
            sum += M[i][p[i]];  // iからp[i]までの重みをsumに加算する
        }
    }
    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 <stdio.h>
#include <math.h>
#include <vector>

using namespace std;

int main(){

	int n,tmp,sum=0,tmp_min;
	scanf("%d",&n);
	int table[n][n],check[n],num_of_group=0,parent,child;
	vector<int> Group;

	for(int i=0;i<n;i++){
		for(int k=0;k<n;k++){
			scanf("%d",&tmp);
			table[i][k]=tmp;
		}
		check[i]=0;
	}

	Group.push_back(0);
	check[0]=1;
	num_of_group = 1;
	while(num_of_group<n){
		tmp_min=2001;

		for(int i=0;i<num_of_group;i++){
			for(int k=0;k<n;k++){
				if(table[Group[i]][k]!=-1&&check[k]==0&&table[Group[i]][k]<tmp_min){
					tmp_min = table[Group[i]][k];
					parent=Group[i];
					child = k;
				}
			}
		}
		Group.push_back(child);
		sum+=table[parent][child];
		check[child]=1;
		num_of_group++;
	}

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

    return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <list>
#include <stack>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
#include <cstdlib>
#define INT_MAX 2147483647
#define INT_MIN -2147483646
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#define Loop1(i, n) for(int i = 1; i <= (int)n; i++)
#define Loopr(i, n) for(int i = (int)n - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = (int)n; i >= 1; i--)
using namespace std;
typedef long long int ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
 
static const int N = 105;
 
struct vertex {
    int id;
    int d;
    bool operator<(const vertex & another) const {
        return (d != another.d ? d>another.d : id>another.id);
    }
};
 
int main() {
    vvi mx(N, vi(N, -1));
    int n;
    cin >> n;
    Loop(i, n) {
        Loop(j, n) {
            int a;
            cin >> a;
            mx[i][j] = a;
        }
    }
     
    vector<bool> color(N, 0);
    priority_queue<vertex> pq;
    pq.push({ 0,0 });
    int cnt = 0;
    int ret = 0;
    while(pq.size() > 0) {
        if (cnt == n) break;
        vertex v = pq.top();
        pq.pop();
        if (color[v.id] == 1) continue;
        color[v.id] = 1;
	cnt++;
        ret += v.d;
        Loop(j, n) {
            if (mx[v.id][j] != -1 && color[j] != 1){
                pq.push({ j, mx[v.id][j] });
            }
        }
    }
    cout << ret << endl;
    return 0;
}

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;
}