Go: package main

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

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

C++: #include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef stack<int> SI;
typedef queue<int> QI;
typedef pair<int,int> PII;
typedef long long LL;

#define d(x)  cout<<#x<<" = "<<(x)<<endl;
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define REACH(i,c) for(typeof((c).rbegin()) i=(c).rbegin(); i!=(c).rend(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c,n) sort(c,c+n)
#define VSORT(c) sort((c).begin(),(c).end())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define DFOR(i,b,a) for(int i=(b)-1;i>=(a);--i)
#define DREP(i,n) DFOR(i,n,0)
#define INF 2000000000

const double EPS = 1e-10;
const double PI  = acos(-1.0);
////////////////////////////////////////////////
int a[100][100],n,s,judge,cost;
int t[100];
int main()
{
	cin>>n;
	REP(i,n)
	{
		REP(j,n)
		{
			cin>>a[i][j];
			if(a[i][j]==-1)a[i][j]=INF;
		}
	}
	t[0]=1;
	for(;;)
	{
		int mincost=INF;
		REP(u,n)
		{
			REP(v,n)
			{
				if(t[u]==1&&t[v]==0)
				{
					if(mincost>a[u][v])
					{
						mincost=a[u][v];
						s=v;
					}
				}
			}
		}
		cost+=mincost;
		t[s]=1;
		judge=1;
		REP(i,n)judge&=t[i];
		if(judge==1)break;
	}
	cout<<cost<<endl;
	return 0;
}

C++: #include <algorithm>
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
#define ll long long
#define ld long double
#define INF 1000000000000000000
typedef pair<ll, ll> pll;
typedef pair<int, int> pint;

struct edge {
    ll to;
    ll cost;
};

int N;
vector<vector<edge>> G;
vector<bool> seen;

ll prim() {
    priority_queue<pll, vector<pll>, greater<pll>> que;
    que.push({0, 0});
    ll ans = 0;

    while (!que.empty()) {
        pll p = que.top();
        que.pop();
        ll v = p.second;
        if (seen[v])
            continue;
        ans += p.first;
        seen[v] = true;
        for (int i = 0; i < G[v].size(); i++) {
            edge e = G[v][i];
            if (!seen[e.to])
                que.push({e.cost, e.to});
        }
    }
    return ans;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> N;
    G.resize(N);
    seen.resize(N, false);
    rep(i, N) {
        rep(j, N) {
            ll a;
            cin >> a;
            if (a == -1)
                continue;
            else
                G[i].push_back({j, a});
        }
    }

    cout << prim() << endl;
}

C++: # include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
typedef pair<LL, LL> pii;
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(ALL((wpwpw)));(wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)
# pragma warning(disable:4996)

int V;
int E;
struct edge { int from, to, cost; };

typedef pair<int, int> PP;

vector<edge> e;

int Par[100000];
int Rank[100000];

void init(int n) {
	for (int i = 0; i < n; i++) {
		Par[i] = i;
		Rank[i] = 0;
	}
}

int find(int x) {
	if (Par[x] == x) {
		return x;
	}
	else {
		return Par[x] = find(Par[x]);
	}
}

void unite(int  x, int y) {
	x = find(x);
	y = find(y);
	if (x == y) return;
	if (Rank[x] < Rank[y]) {
		Par[x] = y;
	}
	else {
		Par[y] = x;
		if (Rank[x] == Rank[y])Rank[x]++;
	}
}

bool same(int x, int y) {
	return find(x) == find(y);
}

// ソート時に比較するための関数 
bool comp(const edge& e1, const edge& e2) {
	return e1.cost < e2.cost;
}

int kruskal() {
	init(V);
	sort(e.begin(), e.end(), comp);
	int ans = 0;
	for (int i = 0; i<E; i++) {
		if (!same(e[i].from, e[i].to)) {
			unite(e[i].from, e[i].to);
			ans += e[i].cost;
		}
	}
	return ans;
}

int main() {
	cin >> V;
	REP(i, V)REP(j, V) {
		int num;
		cin >> num;
		if (num == -1)continue;
		e.emplace_back(edge{(int)i, (int)j, num});
		E++;
	}
	cout << kruskal() << endl;
}