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;
const int MAX = 100;
const int INFTY = 2000000;
const int WHITE = 0;
const int GRAY = 1;
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; i++){
            int e; cin >> e;
            M[i][j] = (e == -1) ? INFTY : e;
        }
    }
    
    cout << prim() << endl;
    
    return 0;
}

C++: //
// Created by tattsun on 2017/02/16.
//

#include <iostream>

#define MAX_N 101
#define INFTY 20000
#define NIL -1

enum Color {
    White,
    Glay,
    Black,
};

using namespace std;

int n;
int w[MAX_N][MAX_N];
int d[MAX_N], p[MAX_N];
Color color[MAX_N];

int min(int x, int y) {
    if(x < y) return x;
    return y;
}

int solve() {
    d[0] = 0;

    while(true) {
        int u = NIL, c = INFTY;

        for(int i=0; i<n; i++) {
            if(d[i] < c && color[i] != Black) {
                u = i;
                c = d[i];
            }
        }

        if(u == NIL)
            break;

        color[u] = Black;

        for(int i=0; i<n; i++) {
            if(color[i] != Black && w[u][i] != INFTY) {
                if(d[i] > w[u][i]) {
                    d[i] = w[u][i];
                    p[i] = u;
                    color[i] = Glay;
                }
            }
        }
    }

    int tc = 0;
    for(int i=0; i<n; i++) {
        if(color[i] == Black) {
            tc += w[i][p[i]];
        }
    }

    return tc;
}

int main() {
    for (int i = 0; i < MAX_N; i++) {
        d[i] = INFTY;
        p[i] = INFTY;
        color[i] = White;
        for (int j = 0; j < MAX_N; j++)
            w[i][j] = INFTY;
    }

    int p;
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> p;
            w[i][j] = (p == -1) ? INFTY : p;
        }
    }

    cout << solve() << endl;
}

C++: #include<iostream>
using namespace std;
const int MAX=105;
const int INF= 1<<30;
int M[MAX][MAX],n,d[MAX],p[MAX],vis[MAX];
void init(){
	for(int i=0;i<n;i++){
		d[i]=INF;
		p[i]=-1;
		vis[i]=0;
	}
	d[0]=0;
}
int Prim(){
	init();
	while (true){
		int u=-1;
		int minCost=INF;
		for(int i=0;i<n;i++){
			if(!vis[i] && d[i]<minCost){
				u=i;
				minCost=d[i];
			}
		}
		if(u==-1)break;
		vis[u]=1;
		for(int i=0;i<n;i++){
			if(!vis[i] && M[u][i]!=-1 &&M[u][i]<d[i]){
				d[i]=M[u][i];
				p[i]=u;
			}
		}
	}
	int sum=0;
	for(int i=0;i<n;i++){
		sum+= (p[i]==-1)?0:M[i][p[i]];
	}
	return sum;
}
int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin>>M[i][j];
		}
	}
	cout<<Prim()<<endl;
	return 0;
}

C++: #include <iostream>
#include <utility>
#include <algorithm>
using namespace std;

int m,n,x,ans;
int P[100+10],edge1[2000+10],edge2[2000+10];


int root(int a){
	if (P[a] == a) return a;
	return (P[a] = root(P[a]));
}

bool same(int a, int b){
	return root(a)==root(b);
}
	
void unite(int a, int b){
	P[root(a)] = root(b);
}

int main() {
	pair<int,int> edges[2000+10];
	cin >> n;
	
	for (int i=1; i<=n; i++){
		P[i] = i;
	}
	
	m = 0;
	for (int i=1; i<=n; i++){
		for (int j=1; j<=n; j++){
			cin >> x;
			if (x>-1){
				edge1[m] = i;
				edge2[m] = j;
				edges[m] = make_pair(x, m);
				m+=1;
			}
		}
	}
	
	sort(edges, edges+m);
	
	for (int i=0; i<m; i++){
		if (!same(edge1[edges[i].second], edge2[edges[i].second])){
			unite(edge1[edges[i].second], edge2[edges[i].second]);
			ans += edges[i].first;
		}
	}
	
	cout << ans << endl;
	
}