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 <vector>
#include <queue>
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[u][v]?????°???u??°v???????????????
int M[MAX][MAX];

struct segment{
    //??????
    int start;
    //??????
    int end;
    //??????
    int dis;

    segment(int s,int e,int d):start(s),end(e),dis(d){}

    bool operator < (const segment& p)const {
        return dis<p.dis;
    }
};

int prim(){
    //????????¶???
    int u=0;
    //??¨?????°???MST?????¶???V?????¶??????
    int p[MAX];
    //??¨?????°???v???????????¶???WHITE???GRAY???BLACK
    int color[MAX];
    //??¨?????°????????\T?????¶??????V-T?????¶?????????????????????????°????????????????
    priority_queue<segment,vector<segment> > d;

    //init
    for(int i=0;i<n;i++){
        p[i]=-1;
        color[i]=WHITE;
    }

    while(true){
        bool ok=true;
        for(int i=0;i<n;i++)
            if(color[i]==WHITE){
                ok= false;
                break;
            }
        if(ok)
            break;

        color[u]=BLACK;
        for(int i=0;i<n;i++)
            if(i!=u&&color[i]==WHITE&&M[u][i]!=INFTY){
                color[i]=GRAY;
                d.push(segment(u,i,M[u][i]));
            }
        u=d.top().end;
        p[u]=d.top().start;
        d.pop();
    }

    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;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0; i<(n); i++)

#define NIL -1
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 1 << 21

int prim(vector<vector<int> > &graph, int n){

    vector<int> parent(n, NIL);
    vector<int> cost(n, INF);
    vector<int> color(n, WHITE);

    cost[0] = 0;
    while(1){
        int minv = INF;
        int u = NIL;
        rep(i, n){
            if(cost[i] < minv && color[i] != BLACK){
                minv = cost[i];
                u = i;
            }
        }
        if(u == NIL) break;

        color[u] = BLACK;
        rep(j, n){
            if(color[j] != BLACK && graph[u][j] != NIL){
                if(cost[j] > graph[u][j]){
                    cost[j] = graph[u][j];
                    parent[j] = u;
                    color[j] = GRAY;
                }
            }
        }
    }

    int sum = 0;
    rep(i, n){
        if(parent[i] != NIL){
            sum += graph[i][parent[i]];
        }
    }
    return sum;
}

int main() {

    int n;
    cin >> n;
    vector<vector<int> > graph(n, vector<int>(n));
    rep(i, n){
        rep(j, n){
            cin >> graph[i][j];
        }
    }

    cout << prim(graph, n) << endl;

    return 0;
}

C++: #include <cstdio>
#include <vector>
#include <algorithm>
#include <queue>

using namespace std;

template <class T>
using gp_queue=priority_queue<T, vector<T>, less<T>>;

using Weight=int;
using DArray=vector<Weight>;
using DMatrix=vector<DArray>;

static const Weight INF=1<<29;

struct Edge {
    size_t src, dst;
    Weight weight;
    Edge() {}
    Edge(size_t src, size_t dst, Weight weight=1):
        src(src), dst(dst), weight(weight)
    {}
};

bool operator<(const Edge &e, const Edge &f) {
    if (e.weight != f.weight) {
        return e.weight > f.weight;
    } else {
        return e.src!=f.src? e.src<f.src : e.dst<f.dst;
    }
}

using Edges=vector<Edge>;
using Vertex=vector<Edge>;
using Graph=vector<Vertex>;

void join(Graph &g, size_t s, size_t d, Weight w=1) {
    // non-directed
    g[s].push_back(Edge(s, d, w));
    g[d].push_back(Edge(d, s, w));
}

void connect(Graph &g, size_t s, size_t d, Weight w=1) {
    // directed
    g[s].push_back(Edge(s, d, w));
}

pair<Weight, Edges> minimum_spanning_tree(const Graph &g, size_t s=0) {
    /* Prim */
    size_t V=g.size();
    Edges T;
    Weight total=0;

    vector<bool> visited(V);
    gp_queue<Edge> q; q.push(Edge(-1, s, 0));
    while (!q.empty()) {
        Edge e=q.top(); q.pop();
        if (visited[e.dst]) continue;

        T.push_back(e);
        total += e.weight;
        visited[e.dst] = true;
        for (const Edge &f: g[e.dst])
            if (!visited[f.dst])
                q.push(f);
    }

    return make_pair(total, T);
}

int main() {
    size_t n;
    scanf("%zu", &n);

    Graph g(n);
    for (size_t i=0; i<n; ++i)
        for (size_t j=0; j<n; ++j) {
            Weight a;
            scanf("%d", &a);

            if (a > -1)
                connect(g, i, j, a);
        }

    printf("%d\n", minimum_spanning_tree(g).first);
    return 0;
}

C++: #include <iostream>
#include<cstdio>
using namespace std;
const int INF = 20001;
static int G[100][100];

int prim(int n){
    
    const int BLACK = 2,GRAY = 1,WHITE =  0;
    int color[n],d[n];
    for(int i = 0;i < n;++i){
        d[i] = INF;
        color[i] = WHITE;
    }
    d[0] = 0;
    int min = INF,u;
    while(1){
        int min = INF;
        for(int i=0;i < n;++i){
            if(color[i] != BLACK && d[i] < min){
                min = d[i];
                u = i;
            }
        }
        if(min == INF) break;
        color[u] = BLACK;
        for(int i=0;i < n;++i){
            if(color[i] != BLACK && G[u][i] != INF){
                if(d[i] > G[u][i]){
                    d[i] = G[u][i];
                    color[i] = GRAY;
                }
            }
        }
        //for(int i = 0;i < n;++i) printf("%d ",d[i]);
    }
    int sum = 0;
    for(int i = 0;i < n;i++) sum += d[i];
    return sum;
}

int main(void){
    int n;
    scanf("%d",&n);
    for(int i = 0;i < n;++i){
        for(int j = 0;j < n;++j){
            scanf("%d",&G[i][j]);
            G[i][j] = (G[i][j] == -1) ? INF:G[i][j];
        }
    }

    printf("%d\n",prim(n));
    
}