Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] > 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A > edges[j].A })

	sum := 0
	for len(edges) > 0 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

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;
}