Go: package main

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

type color int

const (
	white color = iota // 未訪問
	mst                // MSTとして確定
)

// 頂点
type node struct {
	matrix   []int // 隣接行列
	minToMst int   // MSTへの重み最小値
	parent   int   // 最小値の相手
	color    color
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n := eGetInt(scanner)

	nodes := make([]node, n)
	for i := 0; i < n; i++ {
		nodes[i].matrix = eAtoi((strings.Fields(eGetline(scanner))))
		nodes[i].parent = -1
		nodes[i].minToMst = math.MaxInt16
		nodes[i].color = white
	}

	// 初回はnode[0]がMSTに入るように,minToMstを設定
	nodes[0].minToMst = 0
	for { // 全部チェックするまで

		// どの頂点を新たにMSTに取り込むか
		min := math.MaxInt16
		u := -1
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].minToMst < min {
				u = i
				min = nodes[i].minToMst
			}
		}

		if u == -1 {
			break
		}
		// MSTに追加する頂点決定
		nodes[u].color = mst

		// MSTに属していない頂点それぞれについて,MSTとの最小の重みを更新
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].matrix[u] == -1 {
				// 接してない
				continue
			}
			if nodes[i].matrix[u] < nodes[i].minToMst {
				// node[u]との重みが最小
				nodes[i].minToMst = nodes[i].matrix[u]
				nodes[i].parent = u
			}
		}
	}

	sum := 0
	for _, v := range nodes {
		// node[0]はparentが入っていない
		if v.parent != -1 {
			sum += v.matrix[v.parent]
		}
	}
	fmt.Println(sum)
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include<bits/stdc++.h>
#define INF 0x3f3f3f3f
using namespace std;
const int MAXN = 105;

int m[105][105];
int n,e;

int prim(int s)
{
    int minv,cnt[MAXN],k,ans = 0;
    for(int i = 1; i <= n; ++i)
        cnt[i] = m[s][i];
    cnt[s] = 0;
    for(int i = 1; i < n; ++i)
    {
        minv = INF;
        for(int j = 1; j <= n; ++j)
        {
            if(cnt[j] && cnt[j]<minv)
                minv = cnt[j],k = j;
        }
        cnt[k] = 0;
        ans += minv;
        for(int j = 1; j <= n; ++j)
            if(m[k][j] < cnt[j])
                cnt[j] = m[k][j];
    }
    return ans;
}

int main(void)
{
    cin>>n;
    for(int i = 1; i <= n; ++i)
    {
        for(int j = 1; j <= n; ++j)
        {
            cin>>e;
            m[i][j] = e==-1?INF:e;
        }
    }
    cout<<prim(1)<<'\n';
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
struct edge{
    int u,v,cost;
    bool operator<(const edge& v) const {
        return cost < v.cost;
    }
};
const int INF = 1001001001;
const edge imEg = {-1,-1,INF};
vector<edge> es(10000, imEg);
int V,E;
vector<int> par;
vector<int> rnk;

void init_union_find(int n) {
    par.resize(n);
    rnk.resize(n);
    for(int i=0; i<n; i++) {
        par[i] = i;
        rnk[i] = 0;
    }
}

int find(int x) {
    if(x != par[x]) par[x] = find(par[x]);
    return par[x]; 
}

void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if(x == y) return;
    if(rnk[x] > rnk[y]) par[y] = x;
    else par[x] = y;
    if(rnk[x] == rnk[y]) rnk[y]++;
}

int kruskal() {
    init_union_find(V);
    sort(es.begin(), es.end());
    int res = 0;
    for(int i=0; i<E; i++) {
        edge e = es[i];
        if(find(e.u) != find(e.v)) {
            unite(e.u, e.v);
            res += e.cost;
        }
    }
    return res;
}

int main() {
    cin >> V;
    E = 0;
    for(int i=0; i<V; i++) {
        for(int j=0; j<V; j++) {
            int w;
            cin >> w;
            if(w != -1) {
                struct edge e = {i,j,w};
                es[E] = e;
                E++;
            }
        }
    }
    cout << kruskal() << endl;
    return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>
#include <queue>
#include <set>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <bitset>
#include <climits>
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define RFOR(i,a,b) for (int i=(a)-1;i>=(b);i--)
#define ll long long
#define ull unsigned long long
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
const int INF = 1e9;
const int MOD = 1e9 + 7;

using namespace std;

struct Edge{
	int dist,cost;
	Edge(){}
	Edge(int dist,int cost):dist(dist),cost(cost){}
};
	bool operator<(const Edge& e1, const Edge& e2){
		return e1.cost > e2.cost;
	}


int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
	int n;cin>>n;
	vector<vector<Edge> > edge(n,vector<Edge>());
	REP(i,n){
		REP(j,n){
			int c;
			cin>>c;
			if(c == -1)continue;
			edge[i].push_back(Edge(j,c));
		}
	}
	priority_queue<Edge,vector<Edge>,less<Edge> > que;
	que.push(Edge(0,0));//from 0
	int ct = 0;
	int ans = 0;
	vector<bool> primed(n,false);
	while(ct < n){
		Edge e = que.top();
		que.pop();
		if(primed[e.dist])continue;
		primed[e.dist] = true;
		ct++;
		ans += e.cost;
		for(auto e2 : edge[e.dist]){
			que.push(e2);
		}
	}
	cout << ans << endl;
  return 0;
}

C++: /*
* @Author: Samson
* @Date:   2018-06-12 18:24:44
* @Last Modified by:   Samson
* @Last Modified time: 2018-06-13 12:52:45
*/
//   @URL : http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A
#include<bits/stdc++.h>
#include<algorithm>
#include <cstdlib>
#define INF 0x3f3f3f3f
using namespace std;
typedef long long LL;
const int MAXN = 1e2+10;

int p[MAXN],color[MAXN],a[MAXN][MAXN],t,n,d[MAXN];

int prim()
{
	int minv,u,v;
	memset(p,-1,sizeof p);
	memset(d,INF,sizeof d);

	d[2] = 0;
	int ans = 0;

	while(1)
	{
		minv = INF;
		u = -1;
		for(int i = 1; i <= n; ++i)
		{
			if(minv > d[i] && !color[i])
				minv = d[i],u = i;
		}
		if(u == -1)	break; //空集
		color[u] = 1; //从集合中删除
		for(int v = 1; v <= n; ++v)
		{
			if(!color[v] && a[u][v] != INF)
			{
				if(d[v] > a[u][v])
				{
					d[v] = a[u][v];
					p[v] = u;
				}
			}
		}
	}

	for(int i = 1; i <= n; ++i)
		if(p[i] != -1)
			ans += a[p[i]][i];
	return ans;
}

int main(void)
{
	ios::sync_with_stdio(false); 
	//cin.tie(0);
	cin>>n;
	for(int i = 1; i <= n; ++i)
	{
		for(int j = 1; j <= n; ++j)
		{
			cin>>t;
			a[i][j] = t==-1?INF:t;
		}
	}
	cout<<prim()<<'\n';
	return 0;
}

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

#define MAX_V 10000
#define INF 1e9

typedef pair<int, int> pii; // <cost, to>

int cost[MAX_V][MAX_V]; // cost[u][v]??????e=(u,v)????????????(?????¨???????????´??????INF)
bool used[MAX_V]; // ??????i???X????????????????????????
int V;

int prim() {
  for (int i = 0; i < V; ++i) {
    used[i] = false;
  }
  std::priority_queue<pii, vector<pii>, greater<pii> > que;
  que.push(pii(0, 0));
  int res = 0;

  while (!que.empty()) {
    int cst = que.top().first, v = que.top().second;
    que.pop();
    if (used[v])
      continue;
    used[v] = true;
    res += cst;
    for (int u = 0; u < V; u++)
      que.push(pii(cost[v][u], u));
  }

  return res;
}

int main(){
    cin >> V;
    for(int i=0;i<V;++i){
        for(int j=0;j<V;++j){
            int a;
            cin >> a;
            cost[i][j] = (a == -1 ? INF : a);
        }
    }
    cout << prim() << endl;

    return 0;
}