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 <cstdio>
#include <algorithm>

using namespace std;

const int NMAX = 100;
const int AMAX = 2001;
int A[NMAX][NMAX];
int C[NMAX];
int n;

int MST(int a) {
	C[a] = 1;
	int sum, minv, mina;
	sum = 0;

	while (true) {
		minv = AMAX;
		mina = -1;
		for (int i = 0; i < n; i++) {
			if (C[i] == 0) {
				continue;
			}
			for (int j = 0; j < n; j++) {
				if (C[j] == 1 || A[i][j] == AMAX) {
					continue;
				}
				minv = min(A[i][j], minv);
				if (A[i][j] == minv) {
					mina = j;
				}
			}
		}
		if (minv == AMAX || mina == -1) {
			break;
		}
		C[mina] = 1;
		sum += minv;
	}

	return sum;
}

int main() {
	scanf("%d", &n);

	for (int i = 0; i < n; i++) {
		C[i] = 0;
		for (int j = 0; j < n; j++) {
			scanf("%d", &A[i][j]);
			if (A[i][j] == -1) {
				A[i][j] = AMAX;
			}
		}
	}

	printf("%d\n", MST(0));

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;    using vvi = vector<vi>;
using vb = vector<bool>;   using vvb = vector<vb>;
using vl = vector<ll>;     using vvl = vector<vl>;
using vd = vector<double>; using vvd = vector<vd>;

#define REP(i,n) for(auto i = 0 * n; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()
#define FOR(i,s,e) for (ll i = s; i < (ll)e; i++)
#define TEN(x) ((ll)1e##x)

class UnionFind {
	typedef size_t U;
	vector<int32_t> v;
public:
	UnionFind(U n) : v(n, -1) {}
	U find(U x) { return v[x] < 0 ? x : (v[x] = find((U)v[x])); }
	bool same(U x, U y) { return find(x) == find(y); }
	U size(U x) { return (U)-v[find(x)]; }
	void unite(U x, U y) {
		x = find(x); y = find(y);
		if (x != y) {
			if (-v[x] < -v[y]) swap(x, y);
			v[x] += v[y];
			v[y] = x;
		}
	}
};

struct Edge{ uint32_t to, id; };
typedef vector<vector<Edge>> Graph;

template<class T> struct Kruskal{
	typedef uint32_t U;
	template<class V> Kruskal(U n, const V & u, const V & v, const vector<T> & w) : g(n) {
		vector<U> es(w.size());
		iota(es.begin(), es.end(), 0);
		sort(es.begin(), es.end(), [&](U i, U j) { return w[i] < w[j]; });
		UnionFind uf(n);
		for (U i : es) {
			if (!uf.same(u[i], v[i])) {
				uf.unite(u[i], v[i]); cost += w[i];
				g[u[i]].push_back({v[i], i}); g[v[i]].push_back({u[i], i});
			}
		}
	}
	Graph g; T cost = 0;
};

int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(50);

	ll n; cin >> n;
	vl u, v, w;
	REP(i, n) REP(j, n) {
		ll x; cin >> x;
		if (x != -1) {
			u.push_back(i);
			v.push_back(j);
			w.push_back(x);
		}
	}
	Kruskal<ll> mst(n, u, v, w);
	cout << mst.cost << endl;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int Maxn = 110;
static const int INFTY = (1 << 21);
static const int WHITE = 0;
static const int BLACK = 1;

int n, a[Maxn][Maxn], color[Maxn], p[Maxn], d[Maxn];

int prim(){
	for(int i = 0; i < n; i++){
		d[i] = INFTY; p[i] = -1;
	}
	d[0] = 0;
	while(1){
		int minv = INFTY, u = -1;
		for(int i = 0; i < n; i++){
			if(d[i] < minv && color[i] != BLACK){
				minv = d[i];
				u = i;
			}
		}
		if(u == -1) break;
		color[u] = BLACK;
		for(int i = 0; i < n; i++){
			if(a[u][i] < d[i] && color[i] != BLACK){
				d[i] = a[u][i];
				p[i] = u;
			}
		}
	}
	int sum = 0;
	for(int i = 1; i < n; i++) sum += a[i][p[i]];
	return sum;
}
int main()
{
	cin >> n;
	for(int i = 0; i < n; i++){
		for(int j = 0; j < n; j++){
			cin >> a[i][j];
			a[i][j] = (a[i][j] == -1) ? INFTY : a[i][j];  
		} 
	}
	cout << prim() << endl;
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(),(x).end()
const int mod=1000000007,MAX=105,INF=1<<30;
int state[MAX],N,S[MAX][MAX];
priority_queue<pair<int,int>> Q;

int prim(){
    int sum=0,cnt=1;
    for(int i=0;i<N;i++){
        state[i]=0;
    }
    state[0]=1;
    for(int i=0;i<N;i++){
        if(S[0][i]!=INF) Q.push(make_pair(-S[0][i],i));
    }
    while(1){
        int a=Q.top().first;
        int b=Q.top().second;
        Q.pop();
        if(state[b]==0){
            sum+=-a;
            state[b]=1;
            cnt++;
            for(int i=0;i<N;i++){
                if(S[b][i]!=INF&&state[i]==0) Q.push(make_pair(-S[b][i],i));
            }
        }
        if(cnt==N) break;
    }
    return sum;
}



int main(){
    
    cin>>N;
    for(int i=0;i<N;i++){
        for(int j=0;j<N;j++){
            int a;cin>>a;
            if(a==-1) S[i][j]=INF;
            else S[i][j]=a;
        }
    }
    cout<<prim()<<endl;

}