Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

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

const int inf=0x3f3f3f3f;
int G[110][110];
int d[110];
bool vis[110];
int n;

void Dijsktra(){
    d[0]=0;
    for(int i=0;i<n;i++){
        int u=-1,minn=inf;
        for(int j=0;j<n;j++){
           // if(d[j]<minn&&vis[j]==false){
           if(d[u]<minn&&vis[u]==false){
                u=j;
                minn=d[j];
            }
        }
        if(u==-1)
            return ;
        vis[u]=true;
        for(int v=0;v<n;v++){
            if(vis[v]==false&&G[u][v]!=-1&&d[u]+G[u][v]<d[v]){
                d[v]=d[u]+G[u][v];
            }
        }
    }
}

int prim(){
    d[0]=0;
    int ans=0;
    for(int i=0;i<n;i++){
        int u=-1,minn=inf;
        for(int j=0;j<n;j++){
           // if(d[j]<minn&&vis[j]==false){
           if(d[j]<minn&&vis[j]==false){
                u=j;
                minn=d[j];
            }
        }
        if(u==-1)
            return -1;
        vis[u]=true;
        ans+=d[u];
        for(int v=0;v<n;v++){
            if(vis[v]==false&&G[u][v]!=-1&&G[u][v]<d[v]){
                d[v]=G[u][v];
            }
        }
    }
    return ans;
}

int main(){
    //fill(G[0],G[0]+110*110,inf);
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            scanf("%d",&G[i][j]);
        }
    }
    //memset(d,0,sizeof(d));
    memset(vis,0,sizeof(vis));
    fill(d,d+110,inf);
    printf("%d\n",prim());

    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++: #if 0
????????£????????????1.5h
??¢?????????????????§??????????????¢??°????????£????????????sum????¨??????¨????????????????????£????????§?????????
???????????¢??????????????§????????????????????????????????????"-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[100000+10];
	for(int i=0;i<M;i++)
		edges[i]=make_pair(cost[i],i); //first???????????????second???ID
	sort(edges,edges+M);
	
	//for(int i=0;i<M;++i)
		//cout<<edges[i].first<<endl;

	init(N);
	int sum=0;
	for(int i=0;i<M;i++){
		if(is_same_set(src[edges[i].second],dst[edges[i].second])==false){
			unite(src[edges[i].second],dst[edges[i].second]);
			sum+=edges[i].first;
		}
	}
		cout<<sum<<endl;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

struct edge{
	int u;	//?????????
	int v;	//??°??????
	int cost;	//??????
	//???????????????????????§?????§?°???¢????????????
	bool operator<(const edge& another) const {
			return cost < another.cost;
	}
};

const int MAX_N = 100;
const int MAX_M = 10000;

edge es[MAX_M];
int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[i] = 0;
	}
}

int find(int x){		//??¨??????????±???????
	if(par[x] == x){
		return x;
	}else{
		return par[x] = find(par[x]);
	}
}

void unite(int x,int y){	//x???????????¨??¨y???????????¨?????????
	x = find(x);	//x???????????¨??????????????????x??¨??????
	y = find(y);	//y???????????¨??????????????????y??¨??????
	if(x == y) return;
	if(rank[x] < rank[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(rank[x] == rank[y])
			rank[x]++;
	}
}

bool same(int x,int y){	//x,y???????????¨???????????§?????????
	return find(x) == find(y);
}

bool comp(const edge& e1,const edge& e2){
	return e1.cost < e2.cost;
}

int kruskal(int n,int m){
	initial(n);
	int res = 0;
	for(int i=0;i<m;i++){
		edge e = es[i];
		if(!same(e.u,e.v)){
			unite(e.u,e.v);
			res += e.cost;
		}
	}
	return res;
}

int main(){
	int n,m=0,k,l,x;
	cin >> n;	//????????°?????\???
	int cnt=0;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin >> x;
			if(x != -1){
				edge e;
				e.u = i; e.v = j; e.cost = x;
				es[m] = e;
				m++;
			}
		}
	}
	sort(es,es+m);
	cout << kruskal(n,m) << "\n";
}