Go: package main

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

const (
	MAX   = 100
	INFTY = 1 << 21
	NIL   = -1
)

const (
	WHITE = iota
	GRAY
	BLACK
)

type Graph [MAX][MAX]int

func (g *Graph) prim(n int) int {
	var (
		u, minv     = 0, 0
		d, p, color [MAX]int
	)

	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}
	d[0] = 0

	for {
		minv = INFTY
		u = -1
		for 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 v := 0; v < n; v++ {
			if color[v] != BLACK && g[u][v] != INFTY {
				if d[v] > g[u][v] {
					d[v] = g[u][v]
					p[v] = u
					color[v] = GRAY
				}
			}
		}
	}

	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += g[i][p[i]]
		}
	}

	return sum
}

func answer(reader io.Reader) string {
	sc := bufio.NewScanner(reader)
	sc.Split(bufio.ScanWords)

	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	var g Graph
	for i := 0; i < n; i++ {
		for j := 0; j < n; j++ {
			sc.Scan()
			e, _ := strconv.Atoi(sc.Text())
			if e == -1 {
				g[i][j] = INFTY
				continue
			}
			g[i][j] = e
		}
	}

	return fmt.Sprint(g.prim(n))
}

func main() {
	fmt.Println(answer(os.Stdin))
}

C++: #include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

struct Path{
    int w,s,t;
    
    bool operator < (const Path &a) const{
        return w < a.w;
    }
};

struct UnionFind{
    vector<int> par;
    
    UnionFind(int n)
        :par(n)
    {
        for(int i=0;i<n;i++){
            par[i]=i;
        }
    }
    
    void unite(int x,int y){
        int rx=root(x),ry=root(y);
        if(rx==ry)return;
        else{
            par[rx]=ry;
            return;
        }
    }
    
    int root(int x){
        if(x==par[x])return x;
        else return par[x]=root(par[x]);
    }
};

int main(void){
    int i,j,n,w;
    vector<Path> path;
    Path tmp;
    
    cin>>n;
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            cin>>w;
            if(i>j)continue;
            else if(w!=-1){
                tmp.w=w,tmp.s=i,tmp.t=j;
                path.push_back(tmp);
            }
        }
    }
    
    sort(path.begin(),path.end());
    
    UnionFind tree(n);
    int sum=0;

    for(i=0;i<path.size();i++){
        tmp=path[i];
        if(tree.root(tmp.s)!=tree.root(tmp.t)){
            tree.unite(tmp.s,tmp.t);
            sum+=tmp.w;
        }
    }

    cout<<sum<<endl;
    return 0;
}

C++: //最少全域木
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int G[103][103];
int V;
int NG[103][103];//新しくできるほう
int used[103];
int main(){
	int ans=0;
	cin>>V;
	for(int i=0;i<V;i++){
		for(int j=0;j<V;j++){
		cin>>G[i][j];
		}
	}
	for(int i=0;i<103;i++)for(int j=0;j<103;j++)NG[i][j]=-1;
	used[0]=1;
	for(int i=0;i<V;i++){
		int u=-1,a,b;
		for(int j=0;j<V;j++){
		if(used[j]==0)u=i;
		}
		if(u==-1)break;
		int now=99999999;
		for(int j=0;j<V;j++){
			for(int k=0;k<V;k++){
			if(now>G[j][k]&&G[j][k]!=-1&&used[j]==1&&used[k]==0){
			now=G[j][k];
			a=j,b=k;
			}
			}
		}
		ans+=G[a][b];
		used[b]=1;
		NG[a][b]=G[a][b];
	}
	cout<<ans<<endl;
	return 0;
}

C++: //include
//------------------------------------------
#include <iostream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <limits>
using namespace std;

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define FORR(i,a,b) for(int i=(a);i>(b);i--)
#define REP(i,n)  FOR(i,0,n)

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//debug
//-------------------------------------------
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define INF std::numeric_limits<int>::max()

//typedef
//-------------------------------------------
typedef long long ll;

int n;
int g[101][101];

int prim(int used, int sum) {
    if (used == 0) return sum;

    int tmp = INF;
    int use = -1;
    REP(i, n) {
        if ((used>>i)&1) {
            continue;
        }
        REP(j, n) {
            if (((used>>j)&1) && g[i][j] < tmp) {
                tmp = g[i][j];
                use = j;
            }
        }
    }
    return prim(used&(~(1<<use)), sum + tmp);
}

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

    cin >> n;
    REP(i, n) REP(j, n) {
        cin >> g[i][j];
        if (g[i][j] < 0) g[i][j] = INF;
    }
    int used = (1<<n) - 1;
    cout << prim(used&(~1), 0) << endl;

    return 0;
}

C++: #include <iostream>
#include <set>
#define MAX 2001
using namespace std;
int sum;
void MST(int G[100][100],int n){
    set<int>u;
    set<int>t;
    int min=2001,minj;
    u.insert(0);
    for(int i=1;i<n;i++)
        t.insert(i);
    while(u.size()<n){
        for(set<int>::iterator it_u=u.begin();it_u!=u.end();it_u++)
        {
            for(set<int>::iterator it_t=t.begin();it_t!=t.end();it_t++)
                if(G[*it_u][*it_t]>=0)
                {
                    if(G[*it_u][*it_t]<min)
                    {
                        min=G[*it_u][*it_t];
                        minj=*it_t;
                    }
                }
        }
        sum+=min;
        u.insert(minj);
        t.erase(minj);
        min=MAX;
    }
}
int main()
{
    int n,G[100][100];
    cin>>n;
    for(int i=0;i<n;i++)
        for(int j=0;j<n;j++)
            cin>>G[i][j];
    sum=0;
    MST(G,n);
    cout<<sum<<endl;
    return 0;
}