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<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

#define INF 2000000000

int x[10000][10000];
int MIN[10000];
int p[10000];

int prim(){
    int v,MINX;
    int col[10000];
    for(int i=0;i<n;i++){
        MIN[i]=INF;
        p[i]=-1;
        col[i]=0;
    }
    MIN[0]=0;
    while(true){
        MINX=INF;
        v=-1;
        for(int i=0;i<n;i++){
            if(MINX > MIN[i] && col != 2){
                u=i;
                MINX = MIN[i];
            }
        }
        if(u==-1){
            break;
        }
        color[u]=black;
        for(int k=0;k<n;k++){
            if(color != 0 && x[u][k]!=-1 && MIN[k]>x[u][k]){
                MIN[k]=x[u][k];
                col[k]=1;
            }
        }
    }
    int sum=0;
    for(int i=0;i<n;i++){
        sum += x[i][MIN[i]];
    }
    return sum;
}

int main() {
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
    cout<<prim()<<endl;
	return 0;
}

C++: #include <stdio.h>
int main(){
    int n, i, j, t, a[100][100];
    int u, min, d[100], p[100], v[100];
    scanf("%d", &n);
    for(i = 0; i < n; i++) for(j = 0; j < n; j++) {
        scanf("%d", &t);
        a[i][j] = (t==-1)?1000000000:t;
    }
    for(i = 0; i < n; i++) {
        d[i] = 1000000000;
        p[i] = -1;
        v[i] = 0;
    }
    d[0] = 0;
    while(1) {
        min = 1000000000;
        u = -1;
        for(i = 0; i < n; i++) {
            if(min > d[i] && v[i] != 2) {
                u = i;
                min = d[i];
            }
        }
        if(u == -1) break;
        v[u] = 2;
        for(j = 0; j < n; j++) {
            if(v[j] != 2 && a[i][j] != 1000000000){
                if(d[j] > a[u][j]) {
                    d[j] = a[u][j];
                    p[j] = u;
                    v[j] = 1;
                }
            }
        }
        t = 0;
        for(i = 0; i < n; i++) {
            if(p[i] != -1) t+=a[i][p[i]];
        }
    }
    printf("%d\n", t);
    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;
}

C++: #include <cstdio>
#include <climits>
#include <vector>

int w[100][100];
std::vector<int> mst;
std::vector<int> others;
typedef std::vector<int>::iterator itr;

int minimum(){
    if(others.size()<=0)return 0;
    int candiW=INT_MAX;
    itr candiI;
    for(itr i=mst.begin();i!=mst.end();i++){
        for(itr j=others.begin();j!=others.end();j++){
            if(w[*i][*j]<candiW){
                candiW = w[*i][*j];
                candiI = j;
            }
        }
    }
    mst.push_back(*candiI);
    others.erase(candiI);
    return candiW + minimum();
}

int main(){
    int i, j, n;
    scanf("%d",&n);
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            scanf("%d",&w[i][j]);
            if(w[i][j]==-1)w[i][j]=INT_MAX;
        }
    }
    mst.push_back(0);
    for(i=1;i<n;i++)others.push_back(i);
    printf("%d\n",minimum());
    return 0;
}

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

typedef long long ll;

struct Edge {
    ll s,t;
    ll w;
    bool operator < (const Edge& tgt) const {
	return w > tgt.w;
    }
};

ll Prim(const vector<vector<Edge>>& G) {
    const ll V = G.size();
    priority_queue<Edge> edges;
    
    vector<int> used(V,0);
    edges.push( Edge{-1,0,0} );
    ll ans = 0;
    while( edges.size() ) {
	Edge e = edges.top(); edges.pop();

	if( used[e.t] == 1 ) continue;
	used[e.t] = 1;
	ans += e.w;

	for(auto& nxt : G[e.t]) {
	    if( used[nxt.t] == 1 ) continue;
	    edges.push(nxt);
	}
    }
    return ans;
}


int main () {

    ll V; cin >> V;
    vector<vector<Edge>> G(V);
    for(int i=0; i<V; i++) {
	for(int j=0; j<V; j++) {
	    ll w; cin >> w;
	    if( w != -1 ) {
		G[i].push_back( Edge{i,j,w} );
	    }
	}
    }
    cout << Prim(G) << endl;
    return 0;
}