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<bits/stdc++.h>
using namespace std;
#define rp(i,j) for(long long i=0;i<j;i++)
#define rep(i,j,k) for(long long i=j;i<k;i++)
#define mod 1000000007
#define NIL -1
#define MAX 100
static const int INFTY=(1<<21);
typedef long long ll;
int n,u;
int color[MAX];
int m[MAX][MAX];
int d[MAX],p[MAX];
int prim(){
    rp(i,n){
        color[i]=0;d[i]=INFTY;p[i]=NIL;
    }
    d[0]=0;
    while(1){
        int mincost=INFTY;int u=-1;
        rp(i,n){
            if(color[i]!=2&&d[i]<mincost){
                mincost=d[i];
                u=i;
            }
        }
        if(u==-1)break;
        color[u]=2;
        rp(v,n){
            if(color[v]!=2&&m[u][v]!=INFTY){
                if(m[u][v]<d[v]){
                    d[v]=m[u][v];
                    p[v]=u;
                    color[v]=1;
                }
            }
        }
    }
    int sum=0;
    rp(i,n)if(p[i]!=NIL)sum+=m[i][p[i]];
    return sum;
}
int main(){
    int a;
    cin>>n;
    rp(i,n){
        rp(j,n){
            cin>>a;
            if(a!=-1)m[i][j]=a;
            else m[i][j]=INFTY;
        }
    }
    cout<<prim()<<endl;
}

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

using namespace std;

#define FOR(i,s,e) for((i)=(s);(i)<(int)(e);(i)++)
#define REP(i,e) FOR(i,0,e)

#define all(o) (o).begin(), (o).end()
#define psb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))

typedef long long ll;
typedef pair<int, int> PII;

const double EPS = 1e-10;

typedef struct edge_def {
  int from;
  int to;
  int cost;

  edge_def() {;}
  edge_def(int _from, int _to, int _cost) {
    from = _from;
    to   = _to;
    cost = _cost;
  }
} edge;

const int INF = 1000 * 1000 * 1000;
const int N = 100;
int n;
int ed[N];  //ed[i]:??????i???????°???¨?????¨?????¨?????????????????????????????????i??¨??¨?????¨??????????????????????????????
            //????°???¨?????¨????§?????????????????????????????????£????????????
int u[N];  //??¢???????°???¨?????¨???????????????????????????
vector<edge> es[N];

int prim(int s) {
  int i, j, res = 0;
  priority_queue<PII, vector<PII>, greater<PII > > q;
  memset(u, 0, sizeof(u));
  for (i=0; i<n; i++) ed[i] = INF;
  ed[s] = 0;
  q.push(PII(0, s));

  while (q.size()) {
    PII p = q.top(); q.pop();

    u[p.second] = 1;
    res += p.first;

    int m = INF;
    edge me;
    for (i=0; i<n; i++)
      for (j=0; j<(int)es[i].size(); j++) {
        edge e = es[i][j];
        if (u[e.from] && !u[e.to] && e.cost < m) {
          me = e;
          m = me.cost;
        }
      }
    if (m != INF) {
      q.push(PII(me.cost, me.to)); 
      ed[me.to] = me.cost;
    }
  }

  return res;
}


int main() {
  int i, j;
  scanf("%d ", &n);
  int c;
  for (i=0; i<n; i++)
    for (j=0; j<n; j++) {
      scanf("%d ", &c);
      if (c!=-1) es[i].psb(edge(i,j,c));
    }
  printf("%d\n", prim(0));
  return 0;
}

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

const int MAX=100;
int INFTY=1<<30;
int WHITE=0;
int GRAY=1;
int BLACK=2;

int n,m[MAX][MAX];

void 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]){
				p[v]=u;
				d[v]=m[u][v];
				color[v]=GRAY;
			}
	}
	int sum=0;
	for(int i=0;i<n;i++)
	if(p[i]!=-i) sum+=m[i][p[i]];
	cout<<sum<<endl;
}

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;
		}
	}
	prim();
	return 0;
}