Go: package main

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

const (
	white int = iota
	gray
	black
)
const INFTY int = 2001

var G [][]int
var color []int
var d []int
var p []int
var N int

func prim() int {
	u := 0
	d[u] = 0
	for {
		minCost := INFTY
		for i:=0; i<N; i++ {
			if color[i] != black && d[i] < minCost {
				minCost = d[i]
				u = i
			}
		}

		if minCost == INFTY {
			break
		}

		color[u] = black

		for v:=0; v<N; v++ {
			if color[v] != black && G[u][v] != -1 {
				if G[u][v] < d[v] {
					d[v] = G[u][v]
					p[v] = u
					color[v] = gray
				}
			}
		}
	}
	// sum
	sum := 0
	for i:=0; i<N; i++ {
		if p[i] != -1 {
			sum += G[i][p[i]]
		}
	}
	return sum
}




func initVariable(N int) {
	G = make([][]int, N)
	for i:=0; i<N; i++ {
		G[i] = make([]int, N)
	}
	color = make([]int, N)
	d = make([]int, N)
	p = make([]int, N)
	for i:=0; i<N; i++ {
		d[i] = INFTY
		p[i] = -1
	}
}

func nextInt(scanner *bufio.Scanner) int {
	scanner.Scan()
	num, _ := strconv.Atoi(scanner.Text())
	return num
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	N = nextInt(scanner)
	initVariable(N)
	for i:=0; i<N; i++ {
		for j:=0; j<N; j++ {
			G[i][j] = nextInt(scanner)
		}
	}
	fmt.Printf("%d\n", prim())
}

C++: #include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;

int main() {
	int n;
	scanf("%d", &n);
	
	bool added[n];
	int a[n][n];
	for(int i = 0; i < n; i++){
		for(int j = 0; j < n; j++){
			int buf;
			scanf("%d", &buf);
			a[i][j] = buf==-1 ? INT_MAX : buf;
		}
		added[i] = false;
	}
	added[0] = true;
	
	long total = 0;
	for(;1;){
		bool end = true;
		int minCost = INT_MAX, pi, pj;
		for(int i = 0; i < n; i++){
			if(!added[i]){
				end = false;
				continue;
			}
			for(int j = 0; j < n; j++){
				if(minCost > a[i][j]){
					minCost = a[pi = i][pj = j];
				}
			}
		}
		if(end) break;
		added[pi] = added[pj] = true;
		a[pj][pi] = a[pi][pj] = INT_MAX;
		total += minCost;
	}
	
	printf("%ld\n", total);
	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;
    }
    void dump(){
	cout << s << " --> " << t << " : " << w << endl; 
    }
};

ll Prim(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();

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

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

    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} );
//		G[j].push_back( Edge{j,i,w} );
//		cout << i << " <--> " << j << " : " << w << endl; 
	    }
	}
    }

    ll ans = Prim(G);
    cout << ans << endl;
        
    return 0;
}

C++: #if 0
????????£????????????1.5h
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???????????¢??????????????§????????????????????????????????????"-1"???????????????????????????????????§???????????§????????¨???????°???????????????????
#endif

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

int P[10000+10];

void init(int N){
	for(int i=0;i<=N;++i) P[i]=i;
}
int root(int a){
	if(P[a]==a)return a;
	else return(P[a]=root(P[a]));
}
bool is_same_set(int a,int b){
	return root(a)==root(b);
}
void unite(int a,int b){
	P[root(a)]=root(b);
}
int main(){
	int N;
	cin>>N;
	int A[N][N];
	
	for(int i=0; i<N;i++){
		for(int j=0;j<N;j++){
			cin>>A[j][i]; //???????????\???
		}
	}

	int M = 0; 
	int cost[N*N],src[N*N],dst[N*N];
	for (int r=0; r<N;r++)
		for (int c=0; c<r;c++) //r<c???????§?????????????
			if (A[r][c] > -1) {
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				M += 1;
			}
	pair<int,int> edges[2000+10];
	for(int i=0;i<M;i++)
		edges[i]=make_pair(cost[i],i); //first???????????????second???ID
	sort(edges,edges+M);
	
	init(N);
	int sum=0;
	for(int i=0;i<M;i++){
		if(is_same_set(src[edges[i].second],dst[edges[i].second])){
			unite(src[edges[i].second],dst[edges[i].second]);
			sum+=edges[i].first;
		}
	}
		cout<<sum<<endl;
}

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 = 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 <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using pii = pair<int, int>;

const int INF = 1e9;

int main() {
	int n;
	cin >> n;
	vector<vector<int>> a(n, vector<int>(n));
	rep(i, n) rep(j, n) cin >> a[i][j];
	vector<int> mn(n, INF);
	mn[0] = 0;
	vector<bool> used(n, false);
	int ans = 0;
	while (1) {
		int v = -1;
		rep(u, n) if (!used[u] && (v == -1 || mn[u] < mn[v])) v = u;
		if (v == -1) break;
		used[v] = true;
		ans += mn[v];
		rep(u, n) if (a[v][u] != -1) mn[u] = min(mn[u], a[v][u]);
	}
	cout << ans << endl;
	return 0;
}