Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)

int n;
vector<vector<int>> a(100,vector<int>(100, -1));
vector<int> t, d(100, -1);

void prim(int start) {
    t.push_back(start);
    d[start] = 0;
    while (t.size() < n) {
        int min_v = 2001, min_i;
        rep(i, t.size()) {
            rep(j, n) {
                if (a[t[i]][j] != -1 && d[j] == -1 && a[t[i]][j] < min_v) {
                    min_v = a[t[i]][j];
                    min_i = j;
                }
            }
        }
        t.push_back(min_i);
        d[min_i] = min_v;
    }
    
}

int main() {
    scanf("%d", &n);
    rep(i, n) {
        rep(j, n) {
            scanf("%d", &a[i][j]);
        }
    }
    prim(0);
    int sum = 0;
    rep(i, n) {
        sum += d[i];
    }
    printf("%d\n", sum);
}

C++: #include<iostream>
#define INF 1<<30
using namespace std;
int main() {
  int n; cin >> n;
  int graph[101][101] = {};
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j) cin >> graph[i][j];
  int mincost[101], flag[101] = {}, sum = 0;
  for (int i = 2; i <= n; ++i) mincost[i] = INF;
  mincost[1] = 0;
  while (1) {
    int v = -1;
    for (int i = 1; i <= n; ++i) 
      if (!flag[i] && (v == -1 || mincost[v] > mincost[i])) v = i;
    if (v == -1) break;
    flag[v] = 1;
    sum += mincost[v];
    for (int i = 1; i <= n; ++i)
      if (graph[v][i] != -1 && mincost[i] > graph[v][i]) mincost[i] = graph[v][i];
  }
  cout << sum << endl;
  return 0;
}

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

int main() {
    int i, j, n, res = 0;
    cin >> n;
    int a[n][n];

    for (i=0; i<n; i++) {
        for (j=0; j<n; j++) {
            cin >> a[i][j];
        }
    }

    vector<int> v;
    set<int> cons;
    v.push_back(0);
    cons.insert(0);
    while (v.size() != n) {
        int nearest_node = 9999999;
        int nearest_distance = 9999999;
        for (i=0; i<v.size(); i++) {
            for (j=0; j<n; j++) {
                if ((a[v[i]][j] != -1) && (a[v[i]][j] < nearest_distance) && (cons.count(j) == 0)) {
                    nearest_node = j;
                    nearest_distance = a[v[i]][j];
                }
            }
        }
        res += nearest_distance;
        v.push_back(nearest_node);
        cons.insert(nearest_node);
    }
    cout << res << endl;
    return 0;
}

C++: #include <cstdio>
#include <vector>

int main(void){
	int n, min_edge, next_node, count, sum;
	scanf("%d", &n);
	std::vector< std::vector<int> > edges;
	std::vector<int> isUsed;
	edges.resize(n);
	isUsed.resize(n);
	for(int i=0;i<n;i++){
		isUsed[i]=-1;
		edges[i].resize(n);
		for(int j=0;j<n;j++){
			scanf("%d", &edges[i][j]);
		}
	}

	min_edge=3000;
	isUsed[0] = 1;
	count = 0;
	sum=0;
	while(count<4){
		for(int i=0;i<n;i++){
			if(isUsed[i]==1){
				for(int j=0;j<n;j++){
					if (isUsed[j]==-1 && edges[i][j]>-1 && edges[i][j]<min_edge){
						min_edge = edges[i][j];
						next_node = j;
					}
				}
			}
		}
		sum += min_edge;
		isUsed[next_node]=1;
		min_edge = 3000;
		count += 1;
	}
	printf("%d\n", sum);
	return 0;
}

C++: #include<vector>
#include<algorithm>
#include<queue>
#include<stdio.h>
using namespace std;
//结点数最大值 
const int maxn = 1000;
//结点权值最大值 
const int INFTY = 1000000;
//first是下一个结点位置,second是权值 
vector< pair<int,int> > g[maxn];
//parent是父节点,d是当前最短边,is是是否使用过 
int parent[maxn],d[maxn],is[maxn];
//结点数 
int n;
//初始化函数 
void Init(){
	for(int i = 0;i<n;++i){
		//父节点全设置为不存在 
		parent[i] = -1;
		//全设置为最大距离 
		d[i] = INFTY;
		//为输入边和权值做好准备 
		g[i].clear();
		//初始化各边使用状态 
		is[i] = false;
	}
}
int prim(){
	//最小生成树总权值 
	int ans = 0;
	//存储边 
	priority_queue< pair<int,int> >q;
	pair<int,int> work;
	//将0起点的存进去 
	for(int i = g[0].size()-1;i>=0;--i){
		work= g[0][i];
		parent[work.first] = 0;
		//最大堆变最小堆 
		work.second*=-1;
		swap(work.first,work.second);
		q.push(work);
	}
	is[0] = true;
	
	while(q.size()){
		work = q.top();q.pop();
		//to是结点号,v是权值 
		int to = work.second,v = -1*work.first;
		//距离过大或者目标节点已被标记则略过 
		if(d[to]<to||is[to])continue;
		is[to] = true;
		//展示选择的边 
		//printf("%d --> %d:%d\n",parent[to],to,v);
		ans+=v;
		//将当前结点to的边加进队列 
		for(int i  = g[to].size()-1;i>=0;--i){
			work= g[to][i];
			//如果权值比当前的还要大或者目标结点已经被标记过了则跳过 
			if(is[work.first]||d[work.first]<work.second)continue;
			parent[work.first] = to;
			work.second*=-1;
			swap(work.first,work.second);
			q.push(work);
		}
	}
	return ans;
}
int main(){
	int m,a,b,c;
	scanf("%d",&n);
	Init();
	for(int i = 0;i<n;++i){
		for(int j = 0;j<n;++j){
		scanf("%d",&a);
		if(a==-1)continue; 
		g[i].push_back(make_pair(j,a));
		}
	}
	printf("%d\n",prim());
	return 0;
}
//test:
/*
6 10
0 1 2
0 3 1
1 3 3
1 2 1
1 4 2
3 2 2
3 5 2
2 4 5
2 5 3
4 5 1
*/

C++: #define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#define USE_LLONG_AS_INT
#ifdef USE_LLONG_AS_INT
#define int long long
#define inf (1ll<<60)
#else
#define inf (1<<30)
#endif
#define rep(i,n) for(int i=0;i<(n);i++)
#define Rep(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,a,b) for(int i=(a);i<=(b);i++)
#define rev(i,n) for(int i=(n)-1;i>=0;i--)
#define vi vector<int>
#define vvi vector<vi>
#define pb push_back
#define eb emplace_back
#define pi pair<int,int>
#define vp vector<pair<int,int>>
#define mp make_pair
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define MEMSET(a) memset(a,0,sizeof(a))
#define Yes(f) cout<<(f?"Yes":"No")<<endl
#define yes(f) cout<<(f?"yes":"no")<<endl
#define YES(f) cout<<(f?"YES":"NO")<<endl
#define SORT(v) sort(all(v))
#define RSORT(v) sort(all(v), greater<int>())

using namespace std;

const int mod=1e9+7;
const string sp=" ";

void run();

void init() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout<<fixed<<setprecision(12);
}

signed main(){
    init();
    run();
    return 0;
}

int n;
vvi g;

int prim(){
    vi d(n,inf),p(n,-1);
    d[0]=0;
    vector<bool> b(n);
    while(true){
        int u;
        int m=inf;
        rep(i,n){
            if(m>d[i]&&!b[i]){
                u=i;
                m=d[i];
            }
        }
        if(m==inf)break;
        b[u]=true;
        rep(v,n){
            if(!b[v]&&g[u][v]!=inf){
                if(d[v]>g[u][v]){
                    d[v]=g[u][v];
                    p[v]=u;
                }
            }
        }
    }
    int s=0;
    rep(i,n){
        if(p[i]!=-1)s+=g[i][p[i]];
    }
    return s;
}

void run(){
    cin>>n;
    g=vvi(n,vi(n));
    rep(i,n){
        rep(j,n){
            int c;
            cin>>c;
            g[i][j]=c==-1?inf:c;
        }
    }
    cout<<prim()<<endl;
}