Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
const int MAXN = 100 + 4;
const int INF = 0x3f3f3f3f;
const int WHITE = 0;
const int BLACK = 1;
const int GRAY = 2;
int G[MAXN][MAXN];
int d[MAXN], p[MAXN], status[MAXN];
int N;

int prim()
{
    int u, min_d;
    memset ( p, -1, sizeof(p) );
    memset ( status, WHITE , sizeof(status) );
    d[0] = 0;
    for ( int i = 1; i <= N; i++ ) d[i] = INF;

    while ( true ) {
        min_d = INF;
        u = -1;
        for ( int i = 0; i < N; i++ ) {
            if ( min_d > d[i] && status[i] != BLACK ) {
                u = i;
                min_d = d[i];
            }
        }

        if ( u == -1 ) break;
        status[u] = BLACK;
        for ( int v = 0; v < N; v++ ) {
            if ( G[u][v] != INF && status[v] != BLACK ) {
                if ( d[v] > G[u][v] ) {
                    d[v] = G[u][v];
                    p[v] = u;
                    status[v] = GRAY;
                }
            }
        }
    }
    int sum = 0;
    for ( int i = 0; i < N; i++ )
        if ( p[i] != -1 ) sum += G[i][p[i]];

    return sum;
}

int main()
{
    int e;
    cin>>N;
    for ( int i = 0; i < N; i++ ) {
        for ( int j = 0; j < N; j++ ) {
            cin>>e;
            G[i][j] = e == -1 ? INF : e;
        }
    }
    int ans = prim();
    cout<<ans<<endl;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<string>
#include<algorithm>
#include<cmath>
#include<queue>
#include<vector>
#include<stack>
using namespace std;

#define REP(i,n) for(int i=0;(i)<(n);(i)++)
#define ll long long

static const int INFTY = (1 << 25);

int G[100][100], n;

int makeMST() {
	bool mask[100][100];//MAST????????¨???????????¨???????????¨?????????1
	REP(i, n) {
		REP(j, n) mask[i][j] = 0;
	}

	bool color[100];//MST?????\??£??????1
	REP(i, n) color[i] = 0;

	color[0] = 1;//?????????????????¨??????0?????\??????

	REP(k, n - 1) {
		int minv = INFTY;
		int mNodej = -1;
		int mNodei = -1;
		REP(i, n) {
			if (color[i] == 1) {
				REP(j, n) {
					if (G[i][j] != -1) {
						if (color[j] == 0) {
							if (G[i][j] < minv) {
								minv = G[i][j];
								mNodei = i;
								mNodej = j;
							}
						}
					}
				}
			}
		}
		mask[mNodei][mNodej] = 1;
		mask[mNodej][mNodei] = 1;
		color[mNodej] = 1;
	}

	REP(i, n) {
		REP(j, n) {
			if (mask[i][j] == 0) G[i][j] = -1;
		}
	}

	int ans = 0;
	REP(i, n) {
		REP(j, n) {
			if (G[i][j] != -1) ans += G[i][j];
		}
	}

	return ans / 2;
}

int main() {
	cin >> n;

	REP(i, n) {
		REP(j, n) G[i][j] = INFTY;
	}
	REP(i, n) {
		REP(j, n) cin >> G[i][j];
	}

	cout << makeMST() << endl;


	return 0;
}

C++: #include <iostream>
#include <algorithm>
#define N 100
#define INF 2000000000
#define WHITE 0
#define GRAY 1
#define BLACK 2
using namespace std;

int n;
int M[N][N],color[N],d[N],p[N];
   //M??????????????????color????¨??????¶???(0,1,2),d????????????????°???????????¨????
   //p???MST???????°???¨?????¨??????????????????????????????

int Prim() {
	for (int i = 0;i < n;i++) d[i] = INF;
	d[0] = 0;  //?????????????????????????????§???????????§????´???????????????????????????????
	/*p[0] = -1;  //?????????????????????????????????????????? (???????????£????????????)*/

	int u;
	while (true) {
		int min = INF;
		for (int i = 0;i < n;i++) {  //MST????§???????????????????????????????????±????
			if(color[i]!=BLACK&&min>d[i]){
				min = d[i];  //??´??°?????????????????°min?????°??????d[i]???????´??????????????????????...
				u = i;
			}
		}

	if (min == INF) break; //????????\?????????d[i]?????´??°??§???????????¨???????????¨

	color[u] = BLACK;

	for (int v = 0;v < n;v++) 
		if(color[v]!=BLACK&&M[u][v]!=-1)
			if (M[u][v] < d[v]) {
				d[v] = M[u][v];  //?????????????????????????±????
				/*p[v] = u;*/
				/*color[v] = GRAY;(????????????bcSSSP??§?????¢?´¢?????????????????????????????§?????????S)*/
			}

	}

	int sum = 0;
	for (int i = 0;i < n;i++) sum += d[i];  //d[i]???????¨????MST???????????????
	return sum;
		
}

int main() {
	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] = INF;
		}

	cout<<Prim()<<endl;

}

C++: #define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;

//#define int long long
#define DBG 1
#define dump(o) if(DBG){cerr<<#o<<" "<<o<<endl;}
#define dumpc(o) if(DBG){cerr<<#o; for(auto &e:(o))cerr<<" "<<e;cerr<<endl;}
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define each(it,c) for(auto it=(c).begin();it!=(c).end();it++)
#define all(c) c.begin(),c.end()
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9 + 7);
const int W = 0;const int G = 1;const int B = 2;
int n; vector<vector<int>>M;
int prim() {
	int u, minv;
	vector<int>d(n, INF), p(n, -1), color(n, W);
	d[0] = 0;
	while (1) {
		minv = INF;
		u = -1;
		rep(i, 0, n) {
			if (minv > d[i] && color[i] != B) {
				minv = d[i];
				u = i;
			}
		}
		if (u == -1)break;
		color[u] = B;
		rep(v, 0, n) {
			if (color[v] != B&&M[u][v] < d[v]) {
				d[v] = M[u][v];
				p[v] = u;
			}
		}
	}
	int sum(0);
	rep(i, 0, n) {
		if (p[i] != -1)sum += M[i][p[i]];
	}
	return accumulate(d.begin(), d.end(),0);

}
signed main() {
	cin >> n; M = vector<vector<int>>(n, vector<int>(n,INF));
	rep(i, 0, n) {
		rep(j, 0, n) {
			int e; cin >> e;
			M[i][j] = (e == -1) ? INF : e;
		}
	}
	cout << prim() << endl;
	return 0;
}