Go: package main

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

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

C++: #include<cstdio>
#include<queue>
#include<map>
using namespace std;
typedef pair< int, int > Pi;
int info[100][100];
bool used[100];

int prim(const int& V){
  priority_queue< Pi > que;
  que.push(Pi());
  int ret = 0;
  while(!que.empty()){
    Pi p = que.top(); que.pop();
    if(!~-p.first || used[p.second]++) continue;
    ret -= p.first;
    for(int i = 0; i < V; i++) que.push( Pi( -info[p.second][i], i));
  }
  return ret;
}

int main(){
  int N;
  scanf("%d", &N);
  for(int i = 0; i < N; i++){
    for(int j = 0 ; j < N ; j++){
      scanf("%d", &info[i][j]);
    }
  }
  printf("%d\n", prim(N));
}

C++: #include <bits/stdc++.h>
using namespace std;
#define Rep(i, n) for (int i = 0; i < (int)(n); i++)
#define BitRep(i, n) for (int i = 0; i < (int)(1 << n); i++)
#define Sum(vec) accumulate(vec.begin(), vec.end(), 0)
#define Sort(vec) sort(vec.begin(), vec.end())
#define Reverse(vec) reverse(vec.begin(), vec.end())
#define Next_permutation(vec) next_permutation(vec.begin(), vec.end())

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 prime() {
    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 << prime() << endl;
    return 0;
}

C++: #include <bits/stdc++.h>
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];

    // init
    for (int i = 0; i < n; i++) {
        d[i] = INFTY; // ノードごとの最小エッジスコア
        p[i] = -1; // Minimum spanning treeでの親
        color[i] = WHITE;
    }

    d[0] = 0; // node 0からスタート

    while (true) {
        minv = INFTY;
        u = -1;

        // MSTに入っていない点の中で、最小エッジスコアが最小のものを選択 -> u
        for (int i = 0; i < n; i++) {
            if (minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }

        // 行ける範囲にいった場合終わり
        if (u == -1)
            break;
        
        // uに到達
        color[u] = BLACK;

        // uの近傍の最小エッジスコアを更新
        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;
                }
            }
        }
    }

    // back pointerから重みの和を計算
    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 <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <utility>

using namespace std;

#define REP(var, count) for(int var=0; var<count; var++)

struct unionf {
	
	vector<int> data;
	
	unionf(int n) {
		REP(i, n+1) { data.push_back(i); }
	}
	
	int root(int a) {
		if(data[a] == a) { return a; }
		return (data[a] = root(data[a]));
	}
	
	bool issame(int a, int b) {
		return root(a) == root(b);
	}
	
	void unite(int a, int b) {
		data[root(a)] = root(b);
	}

};

int main(void) {
	int N;
	cin >> N;
	
	vector<pair<int, pair<int, int> > > edge;
	
	REP(x, N) {
		REP(y, N) {
			int c;
			cin >> c;
			if ( x <= y ) { continue; }
			if ( c == -1 ) { continue; }
			edge.push_back( make_pair(c, make_pair(x,y)) );
		}
	}
	
	sort(edge.begin(), edge.end());
	
	unionf uf(N);
	
	int cnt = 0;
	int ret = 0;
	REP(i, edge.size() ) {
		
		pair<int, int> sd = edge[i].second;
		if ( ! uf.issame( sd.first, sd.second ) ) {
			cnt ++;
			ret += edge[i].first;
		}
		
		if ( cnt == N-1 ) { break; }
	}
	
	cout << ret << endl;
}

C++: #include<iostream>
using namespace std;
#define S 100
#define INF 2001
#define WHITE 0;
#define GRAY 1;
#define BLACK 2
int n,a[S][S];

int prim(){
    int u,mina;
    int d[S],p[S],cnd[S];

    for(int i=0;i<n;i++){
        d[i]=INF;
        p[i]=-1;
        cnd[i]=WHITE;
    }

    d[0]=0;
    while(1){
        mina=INF;
        u=-1;
        for(int i=0;i<n;i++){
            if(mina>d[i]&&cnd[i]!=BLACK){
                u=i;
                mina=d[i];
            }
        }
        if(u==-1)break;
        cnd[u]=BLACK;
        for(int v=0;v<n;v++){
            if(cnd[v]!=BLACK&&a[u][v]!=INF){
                if(d[v]>a[u][v]){
                    d[v]=a[u][v];
                    p[v]=u;
                    cnd[v]=GRAY;
                }
            }
        }
    }
            int sum=0;
        for(int i=0;i<n;i++){
            if(p[i]!=-1)sum+=a[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;
            if(e==-1)a[i][j]=INF;
            else a[i][j]=e;
        }
    }
    cout<<prim()<<endl;
    return 0;

}