Go: package main

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

const (
	MAX_N      = 200
	MAX_WEIGHT = 2000
)

type Edge struct {
	start  int
	end    int
	weight int
}

type ShortestInfo struct {
	edges    []Edge
	shortest int
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	shortestList := make([]ShortestInfo, n)
	for i := 1; i < n; i++ {
		shortestList[i] = ShortestInfo{edges: []Edge{}, shortest: MAX_N*MAX_WEIGHT + 1}
	}

	adjacentMatrix := make([][]int, n)
	for i := 0; i < n; i++ {
		adjacentMatrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			v, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjacentMatrix[i][j] = v
		}
	}

	mst([]int{1}, shortestList, adjacentMatrix)
	fmt.Println(calculateMinWeight(shortestList))
}

func calculateMinWeight(shortestList []ShortestInfo) int {
	visitedList := make([]bool, len(shortestList))
	visitedList[0] = true
	sumWeight := 0
	for !visitedAll(visitedList) {
		shortestInfo := shortestList[0]
		shortestList = shortestList[1:]
		edges := shortestInfo.edges
		for _, edge := range edges {
			if !visitedList[edge.end-1] {
				visitedList[edge.end-1] = true
				sumWeight += edge.weight
			}
		}
	}
	return sumWeight
}

func visitedAll(visitedList []bool) bool {
	for _, v := range visitedList {
		if !v {
			return false
		}
	}
	return true
}

func mst(nodeStack []int, shortestList []ShortestInfo, adjacentMatrix [][]int) {
	for len(nodeStack) > 0 {
		currentNode := nodeStack[0]
		nodeStack = nodeStack[1:]
		currentShortest := getShortest(currentNode, shortestList)
		adjacents := findAdjacents(currentNode, adjacentMatrix)
		for i := 0; i < len(adjacents); i++ {
			adj := adjacents[i]
			s := getShortest(adj.end, shortestList)
			if currentShortest.shortest+adj.weight < s.shortest || (currentShortest.shortest+adj.weight == s.shortest && len(currentShortest.edges)+1 > len(s.edges)) {
				setShortest(adj.end, adj, currentShortest, shortestList)
				nodeStack = append(nodeStack, adj.end)
			}
		}
	}
}

func getShortest(node int, shortestList []ShortestInfo) ShortestInfo {
	return shortestList[node-1]
}

func setShortest(node int, edge Edge, currentShortest ShortestInfo, shortestList []ShortestInfo) {
	newEdges := make([]Edge, len(currentShortest.edges)+1)
	for i := 0; i < len(newEdges)-1; i++ {
		newEdges[i] = currentShortest.edges[i]
	}
	newEdges[len(newEdges)-1] = edge
	shortestInfo := ShortestInfo{edges: newEdges, shortest: currentShortest.shortest + edge.weight}
	shortestList[node-1] = shortestInfo
}

func findAdjacents(currentNode int, adjacentMatrix [][]int) []Edge {
	adjacents := adjacentMatrix[currentNode-1]
	edges := []Edge{}
	for i, v := range adjacents {
		if v > 0 {
			edges = append(edges, Edge{start: currentNode, end: i + 1, weight: v})
		}
	}
	return edges
}

func nextInt(sc *bufio.Scanner) (int, error) {
	sc.Scan()
	return strconv.Atoi(sc.Text())
}

C++: #include <iostream>
#include <vector>
#include <queue>
#include <cmath>
#include <algorithm>
#include <utility>

using namespace std;

// int search_xyz(int e);
int tree[100];

int root(int a);
bool is_same_set(int p, int q);
void joint(int x, int y);

int main()
{
    int n, tempa, k = 0;
    cin >> n;
    int e = n * (n - 1) / 2;
    pair<int, pair<int, int>

         >
        a[e];
    for (int i = 0; i < n; i++)
    {
        tree[i] = i;
        for (int j = 0; j < n; j++)
        {
            cin >> tempa;
            if (i < j)
            {
                a[k] = make_pair(tempa, make_pair(i, j));
                k++;
            }
        }
    }
    sort(a, a + e);
    int result = 0;
    for (int i = 0; i < e; i++)
    {
        if (a[i].first == -1)
            continue;

        if (is_same_set(a[i].second.first, a[i].second.second))
        {
            continue;
        }
        else
        {
            joint(a[i].second.first, a[i].second.second);
            result += a[i].first;
        }
    }
    cout << result << endl;
    return 0;
}

int root(int a)
{
    if (tree[a] == a)
    {
        return a;
    }
    else
    {
        tree[a] = root(tree[a]);
        return tree[a];
    }
}

bool is_same_set(int p, int q)
{
    return root(p) == root(q);
}

void joint(int x, int y)
{
    tree[root(x)] = root(y);
}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <string>
#include <queue>
using namespace std;
const int MAXN = 10005;
const int INF = 1 << 30;
const int NIL = -1;
struct Node {
	int v, w, next;	//u->v
	friend bool operator<(const Node& a, const Node& b)
	{
		return a.w > b.w;
	}
	Node() {}
	Node(int vv, int ww) : v(vv), w(ww) {}
};
int cnt;
int head[MAXN];
Node edge[MAXN];




int prim(int n)
{
	
	bool vis[MAXN]{ false };
	priority_queue<Node> q;
	vis[1] = true;

	for (int i = head[1]; i != NIL; i = edge[i].next)
		q.push(edge[i]);
	int count = 0;
	int ans = 0;
	Node t;
	while (count < n - 1)
	{
		t = q.top();
		q.pop();
		if (vis[t.v])
			continue;
		vis[t.v] = true;
		ans += t.w;
		++count;
		for (int i = head[t.v]; i != NIL; i = edge[i].next)
			if (!vis[edge[i].v])
				q.push(edge[i]);

	}
	
	return ans;
}


void add(int u, int v, int w)
{
	edge[cnt].v = v;
	edge[cnt].w = w;
	edge[cnt].next = head[u];
	head[u] = cnt++;
}



int main(void)
{
	int n, m, u, v, w;
	scanf("%d", &n);
	int N = n * n;
	for (int i = 0; i <= N; ++i)
		head[i] = NIL;
	cnt = 0;
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= n; ++j)
		{
			scanf("%d", &w);
			if (w != NIL)
				add(i, j, w);
		}
	}
	cout << prim(n) << endl;
	return 0;
}

C++: #include <iostream>
#include <utility>
#include <string>
#include <algorithm>
#include <set>
#include <deque>
#include <vector>
#define MAX 150
#define rep(i,p) for(int i=0;i<p;i++)
#define rep1(i,p) for(int i=1;i<=p;i++)
#define pb push_back
using namespace std;
int n,temp,a,b,size;
int A[MAX];
int B[MAX];
int W[MAX];
int V[MAX];
pair<int,int> edge[MAX];

int root (int child) {
  int a = child;
  while (V[a] != a) {
    a = V[a];
  }
  return a;
}

int main(){
  size = 0;
  cin >> n;
  rep(i,n) 
    rep(j,n) {
      cin >> W[size];
      if (i <= j) {        
        A[size] = i;
        B[size] = j;
        edge[size].first = W[size];
        edge[size].second = size;
        size++;
      }
    }

  // sort by lenght of edge
  sort(edge, edge+size+1);
  // printing
  // rep(i,size+1) {
  //   cout << A[edge[i].second] << " " << B[edge[i].second]
  //        << " " << edge[i].first << endl;;
  // }
  int sum = 0;
  rep(i,n) V[i] = i;
  rep(i,size) {
    if (edge[i].first == -1) continue;
    temp = edge[i].second;
    // a , b : vertex
    a = A[temp]; 
    b = B[temp];
    if (root(a) != root(b)) {
      // ?????????????????????
      sum += edge[i].first;
      if (root(a) != a && root(b) == b){        
        V[b] = a;
      } else if (root(a) == a && root(b) != b) {
        V[a] = b;
      } else if (root(a) == a && root(b) == b) {        
        V[a] = b;
      }
    } else {
    }
  }
  cout << sum << endl;
  return 0;
}