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>

//{ START
using namespace std;
#define int int64_t
#define rep(i, a, n) for (int i = (a); i < (n); ++i)
#define reps(i, a, n) for (int i = (a); i > (n); --i)
#define arep(i, x) for (auto &&i : (x))
#define irep(i, x) for (auto i = (x).begin(); i != (x).end(); ++i)
//降順はgreater<T>()
#define all(x) (x).begin(), (x).end()
#define rv(s) reverse((s).begin(), (s).end())
//gcd lcmはそのままok
#define gcd(a, b) __gcd(a, b)
#define bits(n) (1 << (n))
#define pcnt(x) __builtin_popcountll(x)
//配列内等要素削除
#define unique(x) (x).erase(unique(x).begin(),(x).end()),(x).end())
#define Fixed(n) fixed << setprecision(n)
//総和
#define sowa(n) ((n) * ((n) + 1)) / 2
#define pb(x, a) (x).push_back(a)
#define fb(x, a) (x).push_front(a)
#define eb(x, a) (x).emplace_back(a)
#define F first
#define S second
#define cauto const auto &
using P = pair<int, int>;
using Graph = vector<vector<P>>;
template <class T> //昇順
using min_heap = priority_queue<T, vector<T>, greater<T>>;
template <class T> //降順
using max_heap = priority_queue<T>;
template <class A, class B>
using umap = unordered_map<A, B>;
template <class A>
using uset = unordered_set<A>;
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) //多次元初期化
{
    std::fill((T *)array, (T *)(array + N), val);
}
template <class T>
bool chmax(T &a, const T &b) //最大値更新 返り値はbool
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b) //最小値更新 返り値はbool
{
    if (b < a)
    {
        a = b;
        return 1;
    }
    return 0;
}
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
constexpr int INF = 0x3f3f3f3f;
constexpr int LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr int mod1 = 1e9 + 7;
constexpr int mod2 = 998244353;
//} END

constexpr int MAX_V = 10010;
int cost[MAX_V][MAX_V]; //d[u][v]は辺e=(u,v)のコスト,(存在しないときはINF),d[i][i]=0
int mincost[MAX_V];     //集合xから辺の最小コスト
bool used[MAX_V];       //頂点Iがxに含まれているか
int V;             //頂点数

int prim()
{
    fill(mincost, mincost + V, INF);
    fill(used, used + V, false);
    mincost[0] = 0;
    int res = 0;
    while (true)
    {
        int v = -1;
        //xに属さない頂点のうちxからの辺のコストが最小になる頂点を探す
        rep(u, 0, V)
        {
            if (!used[u] && (v == -1 || mincost[u] < mincost[v]))
                v = u;
        }
        if (v == -1)
            break;
        used[v] = true;    //頂点vをxに追加
        res += mincost[v]; //辺のコストを加える
        rep(u, 0, V) if (cost[v][u] != -1) chmin(mincost[u], cost[v][u]);
    }
    return res;
}

signed main()
{
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    cin >> V;
    rep(i, 0, V) rep(j, 0, V) cin >> cost[i][j];

    cout<<prim()<<'\n';
}

C++: #include <iostream>
#include <list>
#include <utility>
using namespace std;
#define MAXN 100
#define MAXW 2001

int main(){
    int weight[MAXN][MAXN];
    int n; cin >> n;
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
            cin >> weight[i][j];
        }
    }
    
    list<int> MST;
    MST.push_back(0);
    list<int> nonMST;
    for(int i=1; i<n; i++) nonMST.push_back(i);
    
    int weightSum = 0;
    while(!nonMST.empty()){
        int tmpv;
        int tmpWeight = MAXW;
        for(list<int>::iterator it=MST.begin(); it!=MST.end(); it++){
            for(list<int>::iterator it2=nonMST.begin(); it2!=nonMST.end(); it2++){
                if (weight[*it][*it2] < tmpWeight && weight[*it][*it2] != -1){
                    //cout << "tmpWeight update with " << *it2 << endl;
                    tmpWeight = weight[*it][*it2];
                    tmpv = *it2;
                }
            }
        }
        //cout << "MST pushback :" << tmpv << endl; 
        MST.push_back(tmpv);
        nonMST.remove(tmpv);
        weightSum += tmpWeight;
        /*for(list<int>::iterator it=MST.begin(); it!=MST.end(); it++){
            cout << *it << " ";
        }
        cout << endl;
        for(list<int>::iterator it=nonMST.begin(); it!=nonMST.end(); it++){
            cout << *it << " ";
        }
        cout << endl;*/
    }
    
    cout << weightSum << endl;
}