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<stack>
#include<cstdio>
using namespace std;

#define MAX (1<<21)

int n,M[101][101];
int vis[101],d[101],p[101];

int prim(){
    int u,minv,i,v,j;
    for( i = 0; i < n; i++ ){
        d[i] = MAX;
        p[i] = -1;
    }
    d[0] = 0;
    while(1){
        minv = MAX;
        u = -1;
        for( i = 0; i < n; i++ ){
            if( minv > d[i] && !vis[i] ){
                u = i;
                minv = d[i];
            }
        }
        if( u == -1 ) break;
        vis[u] = 1;
        for( v = 0; v < n; v++ ){
            if( !vis[v] && M[u][v] != MAX ){
                if( d[v] > M[u][v] ){
                    d[v] = M[u][v];
                    p[v] = u;
                }
            }
        }
    }
    int sum = 0;
    for( i = 0; i < n; i++ ){
        if( p[i] != -1 ) sum += M[i][p[i]];
    }
    return sum;
}


int main(){
    int i,j,k,m;
    cin >> n;
    for( i = 0; i < n; i++ ){
        for( j = 0; j < n; j++ ){
            cin >> k;
            M[i][j] = (k == -1) ? MAX : k;
        }
    }
    cout << prim() << endl;
}

C++: #include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>
  
#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
  
using namespace std;
  
typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;
  
const int INF=1<<29;
const double EPS=1e-9;
  
const int dx[]={1,0,-1,0,1,1,-1,-1},dy[]={0,-1,0,1,1,-1,-1,1};

class UnionFind {
public:
    int N;
    std::vector<int> parent;
    UnionFind(int n) : N(n), parent(N, -1) {
    }
    void Union(int a, int b) {
        a = root(a);
        b = root(b);
        int sizea = size(a);
        int sizeb = size(b);
        if (sizea > sizeb) {
            int temp = a;
            a = b;
            b = temp;
        }
        parent[b] += parent[a];
        parent[a] = b;
    }
    int root(int a) {
        if (parent[a] < 0) return a;
        return parent[a] = root(parent[a]);
    }
    int size(int a) {
        return -parent[root(a)];
    }
    bool Find(int a, int b) {
        return root(a) == root(b);
    }
};

struct edge {
    int a;
    int b;
    int c;
    bool operator<(const edge &rhs) const {
        return c < rhs.c;
    }
    edge(int a_, int b_, int c_) : a(a_), b(b_), c(c_) {

    }
};

int main() {
    int N;
    cin >> N;

    UnionFind uf(N);
    std::vector<edge> e;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            int c;
            cin >> c;
            if (c == -1) continue;
            e.push_back((edge){i, j, c});
        }
    }

    sort(e.begin(), e.end());

    int ans = 0;
    for (int i = 0; i < e.size(); i++) {
        if (!uf.Find(e[i].a, e[i].b)) {
            uf.Union(e[i].a, e[i].b);
            ans += e[i].c;
        }
    }
    cout << ans << endl;
    return 0;
}

C++: #include<iostream>
#include<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<deque>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;
typedef pair<int, int> P;

int prim(vector<vector<int>> a) {
	int n = a.size();
	priority_queue<P, vector<P>, greater<P>> pq;
	pq.push(P(0, 0));
	set<int> mst;
	int res = 0;
	while (mst.size() < n) {
		int s = pq.top().second;
		res += pq.top().first;
		pq.pop();
		mst.insert(s);
		REP(j, n) {
			if (a[s][j] >= 0 && mst.find(j) == mst.end()) {
				pq.push(P(a[s][j], j));
			}
		}
	}
	return res;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n;
	cin >> n;
	vector<vector<int>> a(n, vector<int>(n));
	REP(i, n)REP(j, n) cin >> a[i][j];

	cout << prim(a) << "\n";
	
	return 0;
}