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>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

int root(int i,vector<int> &parent){
    if(parent[i]==-1){
        //親がいない時
        return i;
    }else{
        int result=root(parent[i],parent);
        parent[i]=result; //パス圧縮
        return result;
    }
}

void unite(int x,int y,vector<int> &parent){
    if(root(x,parent)!=root(y,parent)){
        parent[root(y,parent)]=root(x,parent);
    }
}

bool issame(int x,int y,vector<int> &parent){
    return root(x,parent)==root(y,parent);
}

int main(){
    int n;
    cin >> n;
    //first:cost,second:(first:from,second:to)
    vector<pair<int,pair<int,int> > > bridges(n*n);

    //入力
    for(int i=0;i<n;++i){
        for(int j=0;j<n;++j){
            int cost;
            if(cin >> cost,cost!=-1){
                bridges.push_back(pair<int,pair<int,int> >(cost,pair<int,int>(i,j)));
            }
        }
    }

    //sort
    sort(bridges.begin(),bridges.end());

    //島を管理する用
    vector<int> parents(n*n,-1);

    int sum=0;

    for(int i=0;i<bridges.size();++i){
        if(!issame(bridges[i].second.first,bridges[i].second.second,parents)){
            unite(bridges[i].second.first,bridges[i].second.second,parents);
            sum+=bridges[i].first;
        }
    }
    cout << sum << endl;
}

C++: #include <iostream>
#include <map>
#include <vector>
using namespace std;
typedef vector <int> vi;
typedef vector <vi> vvi;
struct edge{
	int from;
	int to;
};
typedef multimap <int, edge, less<int> > mme;

int addedge(vvi &graph, int y, int x, int val=1){
	graph[y][x] = val;
	return val;
}

int make_graph(vvi &graph, vi &stamp){
	int n=graph.size(), val;

	for (int j=0; j<n; j++){
		for (int i=0; i<n; i++){
			cin>>val;
			addedge(graph, i, j, val);
		}
		stamp[j] = 0;
	}
	return 0;
}

int Minimum_Spanning_Tree(vvi &graph, vi &stamp){

	mme edges;
	int n = graph.size(), p1, p2, p3, total=0;
	p1=0;
	stamp[p1] = 1;

	while (p1!=-1){
		for (int p2=0; p2<n; p2++){
			int *tmp=&graph[p1][p2];
			if (*tmp!=-1 && stamp[p2]==0){
				edge e;
				e.from = p1;
				e.to = p2;
				edges.insert(pair <int, edge> (*tmp, e));
			}
		}
		p1=-1;
		while (! edges.empty()){
			mme::iterator const it = edges.begin();
			if (stamp[it->second.from]==1 && stamp[it->second.to]==0){
				p1 = it->second.to;
				stamp[p1]=1;
				total+=it->first;
				edges.erase(it);
				break;
			}
			edges.erase(it);
		}
	}
	return total;
}

int resultout(vvi &graph){
	for (int i=0; i<int(graph.size()); i++){
		for (int j=0; j<int(graph.size()); j++){
		cout<<graph[i][j]<<" ";
		}
		cout<<endl;
	}
	return 0;
}

int main(void){

	int n, row;
	cin>>n;
	vvi G(n, vi(n));
	vi stamp(n);

	make_graph(G, stamp);

	cout<<Minimum_Spanning_Tree(G, stamp)<<endl;

	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <vector>
#include <set>
#include <string>
#include <queue>
#include <algorithm>
#include <map>
#include <cmath>
#include <list>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#define rep(i, n) for (int i = 0; i < n; i++)

using namespace std;
typedef vector<int> vi;
typedef pair<int, int> pii;

const int INF = 1 << 30;
const int MOD = 1000000007;
const int MAX = 100000;
const int N = 100;

vector<pii> G[N];
bool T[N];

int main() {
	int n; cin >> n;
	rep(i, n) { rep(j, n) {
		int a; cin >> a;
		if (a == -1) continue;
		G[i].push_back(pii(a, j));
	} }
	rep(i, n) T[i] = false;

	int ans = 0;
	priority_queue<pii, vector<pii>, greater<pii>> Q;
	Q.push(pii(0, 0));
	while (!Q.empty()) {
		pii p = Q.top(); Q.pop();
		if (T[p.second]) continue;
		ans += p.first;
		T[p.second] = true;
		for (auto i : G[p.second]) Q.push(i);
	}
	cout << ans << endl;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;

const int NOTV = 0;
const int VIST = 0;
const int NMAX = 100;
const int VMAX = 2000;
const int NILL = -1;
const int INFTY = 1 << 21;
int n;
int a[NMAX][NMAX];  //??£??\??????
int v[NMAX];  //????°???¨?????¨?????????
int d[NMAX];  //????°???¨?????¨??????????????????
int vis[NMAX];
//priority_queue <greater<int>> pq;

int prim() {
	for (int i = 0; i < n; i++) {
		vis[i] = NOTV;
		d[i] = INFTY;
		v[i] = -1;
	}
	d[0] = 0;
	int u = 0;
	while (1) {
		int mincost = INFTY;
		u = -1;
		for (int i = 0; i < n; i++) {
			if (vis[i] == NOTV and mincost > d[i]) {
				mincost = d[i];
				u = i;
			}
		}
		if (u==-1) break;
		vis[u] = VIST;
		for (int ver = 0; ver < n; ver++) {
			if (vis[ver] == NOTV and a[u][ver] != INFTY) {
				if (a[u][ver] < d[ver]) {
					d[ver] = a[u][ver];
					v[ver] = u;
					vis[ver] = NOTV;
				}
			}
		}
		cout << u << endl;
	}
	int ans = 0;
	for (int i = 0; i < n; i++) {
		if (v[i] != -1) ans += a[i][v[i]];
	}
	return ans;
}

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int e;
			cin >> e;
			a[i][j] = e;
			if (a[i][j] == -1) {
				a[i][j] = INFTY;
			}
		}
	}
	
	cout << prim() << endl;
	return 0;
}

C++: #include<bits/stdc++.h>
#define rep(i,n) for(int i=0;i< (n);i++)
using namespace std;
typedef long long ll;
const int INF = 1e+7;

struct prim{
    vector<int> color;
    vector<vector<int>> M;
    vector<int> d;
    vector<int> p;
    int n_;
    prim(int n):color(n,0),M(n,vector<int>(n,-1)),d(n,INF),p(n,-1){
        n_ = n;
    }
    void init(){
        rep(i,n_){
            rep(j,n_){
                int tmp;cin>>tmp;
                M[i][j] = tmp;
            }
        }
    }

    void solve(){
        init();
        d[0] = 0;
        p[0] = -1;

        while(true){
            int mincost = INF;
            int u;
            rep(i,n_){
                if(color[i] != 2 && d[i] < mincost ){
                    mincost = d[i];
                    u = i;
                }
            }
            if( mincost == INF){
                break;
            }
            color[u] = 2;

            rep(v,n_){
                if(color[v] != 2 && M[u][v] != -1){
                    if(M[u][v] < d[v]){
                        d[v] = M[u][v];
                        p[v] = u;
                        color[v] = 1;
                    }
                }
            }
        }
        int ans = 0;
        rep(i,n_){
            ans += d[i];
        }
        cout<<ans<<endl;
    }
};

int main(){
    int n;cin >> n;
    prim p(n);
    p.solve();
    return 0;
}