Go: package main

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

const (
	MAX = 100
	INF = 1 << 21
	WHITE = 0
	GRAY = 1
	BLACK = 2
)

var (
	n int
	M [MAX][MAX]int
)

func prim() int {
	var u, minv int
	var d [MAX]int
	var p [MAX]int
	var color [MAX]int

	for i := 0; i < n; i++ {
		d[i] = INF
		p[i] = -1
		color[i] = WHITE
	}
	d[0] = 0
	for {
		minv = INF
		u = -1
		for 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 v := 0; v < n; v++ {
			if color[v] != BLACK && M[u][v] != INF {
				if d[v] > M[u][v] {
					d[v] = M[u][v]
					p[v] = u
					color[v] = GRAY
				}
			}
		}
	}
	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	n, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < n; i++ {
		for j := 0; j < n; j++ {
			scanner.Scan()
			e, _ := strconv.Atoi(scanner.Text())
			if e == -1 {
				M[i][j] = INF
			} else {
				M[i][j] = e
			}
		}
	}
	fmt.Println(prim())
}

C++: #include <iostream>
#include <climits>
using namespace std;

int n;
int g[101][101];

int d[101];
char c[101];
int p[101];

void prim() {
    for (int i = 0; i < n; ++i) {
        d[i] = INT_MAX;
        c[i] = 'w';
    }
    c[0] = 'b';
    d[0] = 0;
    while (true) {
        int u, v;
        int mine = INT_MAX;
        for (int j = 0; j < n; ++j) {
            if (c[j] == 'b') {
                u = j;
                for (int k = 0; k < n; ++k) {
                    if(g[u][k] > -1 && g[u][k] <= d[k] && c[k] != 'b' && g[u][k] <= mine) {
                        d[k] = g[u][k];
                        mine = d[k];
                        v = k;
                    }
                }
            }
        }
        p[v] = u;
        c[v] = 'b';
        if(mine == INT_MAX) break;
    }
}

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int w;
            cin >> w;
            g[i][j] = w;
        }
    }
    prim();
    int sum;
    for (int k = 0; k < n; ++k) {
        sum += d[k];
    }
    cout << sum << endl;


    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>

using namespace std;

struct edge {
    int from, to, cost;
};

int main() {
    int n;
    cin >> n;

    vector<edge> E;
    int cost;
    for (int i=0; i<n; ++i) {
        for (int j=0; j<n; ++j) {
            cin >> cost;
            if (0 <= cost) {
                E.push_back((edge){ i, j, cost });
            }
        }
    }

    bool used[100] = {};
    used[0] = true;

    int ret = 0;

    while (1) {
        int next = -1;
        int min_cost = INT_MAX;
        for (int i=0; i<(int)E.size(); ++i) {
            edge &e = E[i];
            if (used[e.from] && ! used[e.to] && e.cost < min_cost) {
                next = e.to;
                min_cost = e.cost;
            }
        }
        if (next == -1) break;
        used[next] = true;
        ret += min_cost;
    }

    cout << ret << endl;

    return 0;
}

C++: #include<stdio.h>
#include<algorithm>
#include<queue>
#include<string.h>
using namespace std;
#define NIL -2000000001
#define INFTY 2000000001
#define MAX 101
#define WHITE 0
#define GRAY 1
#define BLACK 2

int n = 0;
int adm[MAX][MAX];
int color[MAX];
int d[MAX], p[MAX];
queue<int> queueBfs;


int mst() {
  int sum = 0;
  for ( int i = 0; i < n; i++ ) {
    color[i] = WHITE;
    d[i] = INFTY;
    p[i] = -1;
  }
  d[0] = 0;

  while (true) {
    int mincost = INFTY;
    int u; //訪問する頂点

    for (int i = 0; i < n; i++) {
      if (color[i] != BLACK && d[i] < mincost) {
        mincost = d[i];
        u = i;
      }
    }
    if (mincost == INFTY) break;
    sum += mincost;
    color[u] = BLACK;

    // u周りの頂点vの情報を入れる
    for (int v = 0; v < n; v++) {
      if (color[v] != BLACK && adm[u][v] != -1 && adm[u][v] < d[v]) {
        d[v] = adm[u][v];
        p[v] = u;
        color[v] = GRAY;
      }
    }
  }

  return sum;
}

int main() {
  scanf("%d", &n);
  for ( int i = 0; i < n; i++ ) {
    for ( int j = 0; j < n; j++) {
      scanf("%d", &adm[i][j]);
    }
  }

  printf("%d\n", mst());
  
  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<tuple>
using namespace std;

int n,m=0,tmp,p[110],ans=0,a,b,c; //m:辺の数
tuple<int,int,int> line[10010]; //辺

void init(int n){ //初期化
    for(int i=0;i<n;i++){p[i]=i;}
}

int root(int a){ //根を求める
    if(p[a]==a){return a;}
    return (p[a]=root(p[a])); //親の根を親とする
}

bool is_same_set(int a,int b){ //根が同じか判定
    return root(a)==root(b);
}

void unite(int a,int b){ //結合
    p[root(a)]=root(b);
}

int main(){
    cin>>n;
    init(n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin>>tmp;
            if(j>i){
                if(tmp!=-1){
                    line[m]=make_tuple(tmp,i,j);
                    m++;
                }
            }
        }
    }
    sort(line,line+m);
    init(n);
    for(int i=0;i<m;i++){
        c=get<0>(line[i]);
        a=get<1>(line[i]);
        b=get<2>(line[i]);
        if(!(is_same_set(a,b))){
            unite(a,b);
            ans+=c;
        }
        //cout<<c<<a<<b<<endl;
    }
    cout<<ans<<endl;
}

C++: #include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<vector>
#include<queue>
using namespace std;

struct Edge{
  int src,dst;
  int weight;
  Edge(int src,int dst,int weight):
    src(src),dst(dst),weight(weight){}
};

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

bool operator < (const Edge &m,const Edge &n){
  return m.weight!=n.weight ? m.weight>n.weight :
    m.src!=n.src ? m.src>n.src : m.dst>n.dst;
}

struct UnionFind{
  vector<int> data;
  UnionFind(int size):
    data(size,-1){}

  int root(int x){
    return data[x]<0 ? x :
      data[x]=root(data[x]);
  }

  void unionset(int x,int y){ //bool->void
    x=root(x);y=root(y);
    if(x!=y){
      if(data[y]<data[x])
	swap(x,y);
      data[x]+=data[y];
      data[y]=x;
    }
    //return x!=y;
  }

  bool findset(int x,int y){
    return root(x)==root(y);
  }
};

/*test用関数
void PrintGraph(Graph);
void PrintEdges(Edges);
void PrintPriority_queue(priority_queue<Edge>);
*/

pair<int,Edges> MinimumSpinningForest(Graph g){
  int n=g.size();
  UnionFind uf(n);
  priority_queue<Edge> que;

  for(int i=0;i<n;i++){
    for(Edges::iterator l=g[i].begin();l!=g[i].end();l++){
      if((*l).src<(*l).dst && (*l).weight>0)
	que.push(*l);
    }
  }

  //PrintPriority_queue(que);
  int sum=0;
  Edges select;

  while((int)select.size()<n && !que.empty()){
    Edge tmp=que.top();que.pop();

    if(!uf.findset(tmp.src,tmp.dst)){
      uf.unionset(tmp.src,tmp.dst);
      select.push_back(tmp);
      sum+=tmp.weight;
    }
  }

  return pair<int,Edges>(sum,select);
}


int main(int argc,char* argv[]){
  Graph g;
  int n,x;
  pair<int,Edges> p;

  cin>>n; 
  for(int i=1;i<=n;i++){
    for(int l=1;l<=n;l++){
      cin>>x;
      Edge tmp(i,l,x);
      Edges input;input.push_back(tmp);
      g.push_back(input);
    }
  }

  //PrintGraph(g);

  p=MinimumSpinningForest(g);

  //PrintEdges(p.second);
  
  cout<<p.first<<endl;
  return 0;
}