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 <bits/stdc++.h>

using namespace std;
using LL = long long;
using P = pair<int, int>;
using Tapris = tuple<int, int, int>;

#define REP(i, n) for(LL i = 0; i < n; ++i)
#define FOR(i, a, n) for(LL i = a; i < n; ++i)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()

const int INF = (int)1e9;
const LL INFL = (LL)1e15;
const int MOD = 1e9 + 7;

int dy[]={0, 0, 1, -1, 0};
int dx[]={1, -1, 0, 0, 0};

//#define int long long
// 0-indexedに注意
template<typename T>
struct Edge {
    int to;
    T cost;
    Edge(int to, T cost) : to(to), cost(cost) {}
};

template<typename T>
class Prim{
    private:
        vector<vector<Edge<T>>> graph;
        vector<bool> used;
    public:
        Prim(int n);
        void AddEdge(int from, int to, T cost);
        T Run();
};

template<typename T>
Prim<T>::Prim(int n): graph(n), used(n, false) {}

template<typename T>
void Prim<T>::AddEdge(int from, int to, T cost){
    graph[from].push_back(Edge<T>(to, cost));
}

template<typename T>
T Prim<T>::Run(){
    using Pi = pair<T, int>;
    T total = 0;
    priority_queue<Pi, vector<Pi>, greater<Pi>> que;
    que.emplace(0, 0);
    while(!que.empty()){
        Pi p = que.top();
        que.pop();
        if(used[p.second]) continue;
        used[p.second] = true;
        total += p.first;
        for(auto &e : graph[p.second]){
            que.emplace(e.cost, e.to);
        }
    }
    return total;
}
/*************** using variables ***************/

/**********************************************/

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int n;
    cin >> n;
    Prim<int> prim(n);
    REP(i, n){
        REP(j, n){
            int x;
            cin >> x;
            if(x != -1) prim.AddEdge(i, j, x);
        }
    }

    cout << prim.Run() << endl;
}

C++: #include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#define ll long long
#define ALL(x) (x).begin(),(x).end()
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define vi vector<int>
#define vvi vector<vector<int>>
using namespace std;

class UnionFind {
private:
    vector<vector<int>> Graph; // {ID,Number,ParentID,Height}

    void flatten(int x, int rootid) {
        int parentid = Graph[x][0];
        while (Graph[parentid][0] != Graph[parentid][2]) {
            Graph[parentid][2] = rootid;
            int next = Graph[parentid][2];
            parentid = next;
        }
    }
public:
    void push(int x) {
        int i = Graph.size();
        Graph.push_back({ i,x,i,1 });
    }
    void unite(int x, int y) {
        int hx = Graph[root(x)][3];
        int hy = Graph[root(y)][3];
        if (hx < hy) {
            Graph[root(x)][2] = root(y);
            flatten(x, root(y));
        }
        else if(hx == hy){
            Graph[root(y)][2] = root(x);
            Graph[root(x)][3]++;
            flatten(y, root(x));
        }
        else {
            Graph[root(y)][2] = root(x);
            flatten(y, root(x));
        }
    }
    bool same(int x, int y) {
        return root(x) == root(y);
    }

   
    int root(int x) {
        int parentid = Graph[x][0];
        while (Graph[parentid][0] != Graph[parentid][2]) {
            int next = Graph[parentid][2];
            parentid = next;
        }
       
        return parentid;
    }
};

int main() {
    int n; cin >> n;
    vector<vector<int>> edges; // {weight, from_id, to_id} both 0-indexed
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int w; cin >> w;
            if (w == -1) {
                continue;
            }
            else {
                vector<int> temp_edge = { w,i,j };
                edges.push_back(temp_edge);
            }
        }
    }

    sort(ALL(edges));
    int n_edges = 0;
    int TotalCost = 0;

    UnionFind uf;
    for (int i = 0; i < n; i++) uf.push(i);

    for (int i = 0; n_edges < n - 1; i++) {
        vector<int> edge = edges[i];
       
        if (uf.root(edge[1]) != uf.root(edge[2])) {
            uf.unite(edge[1], edge[2]);
            n_edges++;
            TotalCost += edge[0];
        }
    }


    cout << TotalCost << endl;
}