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 <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()

typedef long long ll;
typedef pair<int, int> P;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;

class UnionFind {
private:
    int n;
    vector<int> uni;
public:
    UnionFind(int _n) {
        n = _n;
        uni.clear();
        uni.resize(n, -1);
    }
    int root(int x) {
        if (uni[x] < 0) return x;
        return uni[x] = root(uni[x]);
    }
    bool same(int x, int y) {
        return root(x) == root(y);
    }
    void unite(int x, int y) {
        x = root(x);
        y = root(y);
        if (x == y) return;
        if (uni[x] > uni[y]) swap(x, y);
        uni[x] += uni[y];
        uni[y] = x;
    }
    void print() {
        for (auto x : uni) cout << x << " ";
        cout << endl;
    }
};

struct edge {
    int from, to, cost;
    edge(){}
    edge(int _from, int _to, int _cost) : from(_from), to(_to), cost(_cost) {}
    bool operator< (const edge& e) const {
        return cost == e.cost ? (from == e.from ? to < e.to : from < e.from) : cost < e.cost;
    }
};

class Kruskal {
private:
    int n;
    vector<edge> edges;
    UnionFind uf;
public:
    Kruskal(int _n) : n(_n), uf(UnionFind(n)) {
        rep(i, n) {
            rep(j, n) {
                int c;
                cin >> c;
                if (c == -1) c = 1e9;
                edges.emplace_back(i, j, c);
            }
        }
        sort(all(edges));
    }
    int calc() {
        int res = 0;
        for (auto &e : edges) {
            if (!uf.same(e.from, e.to)) {
                uf.unite(e.from, e.to);
                res += e.cost;
            }
        }
        return res;
    }
};

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

    int n;
    cin >> n;
    Kruskal kr(n);
    cout << kr.calc() << endl;
}

C++: #include "bits/stdc++.h"
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>
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;
}