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 <utility>
#include <algorithm>
using namespace std;

int p[100];
pair<int, int> a[10000];

int root( int m ) {
	if ( p[m] != m )
		p[m] = root( p[m] );
	return p[m];
}

void unit( int x, int y ) {
	p[root( y )] = root( x );
}

bool same( int x, int y ) {
	return root( x ) == root( y );
}

int main() {
	int n, ai, pn, ans;
	cin >> n;
	for ( int i = 0; i < n * n; i++ ) {
		cin >> ai;
		if ( ai == -1 || ai % n <= ai / n )
			ai = 2001;
		a[i] = make_pair( ai, i );
	}
	sort( a, a + ( n * n ) );
	pn = 0;
	ans = 0;
	for ( int i = 0; i < n; i++ )
		p[i] = i;
	for ( int i = 0; i < n * n; i++ ) {
		if ( ! same( a[i].second % n, a[i].second / n ) ) {
			ans += a[i].first;
			pn++;
			unit( a[i].second % n, a[i].second / n );
			if ( pn >= n - 1 ) break;
		}
	}
	cout << ans << endl;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <list>
#include <stack>
#include <string>
#include <functional>
#include <numeric>
#define _USE_MATH_DEFINES
#include <math.h>
#include <iomanip>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
using namespace std;
#define INT_MAX 2147483647
#define INT_MIN (-2147483647 - 1)
#define INF (int)1e8
#define _INF (int)-1e8
#define INFLL (long long)1e14
#define _INFLL (long long)-1e14
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#define Loop1(i, n) for(int i = 1; i <= (int)n; i++)
#define Loopr(i, n) for(int i = (int)n - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = (int)n; i >= 1; i--)
#define bitmanip(m,val) static_cast<bitset<(int)m>>(val)
typedef long long int ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef pair<int, int> P;

class MST {
private:
	struct node {
		bool done;
		vi to, cost;
		int id, from;
		ll d;
		bool operator<(const node & another) const {
			return !(d != another.d ? d < another.d : id < another.id);
		}
	};
	vector<node> nodes;
	int n;
public:
	vll result;
	MST(vector<vector<P>> data) {
		n = data.size();
		result.resize(n);
		nodes.resize(n);
		Loop(i, n) {
			nodes[i] = { false,{},{}, i, -1, INFLL };
			Loop(j, data[i].size()) {
				nodes[i].to.push_back(data[i][j].first);
				nodes[i].cost.push_back(data[i][j].second);
			}
		}
	}
	void mainfunc(int start) {
		priority_queue<node> pq;
		nodes[start].d = 0;
		pq.push(nodes[start]);
		while (pq.size()) {
			node a = pq.top(); pq.pop();
			if (nodes[a.id].done) continue;
			nodes[a.id].done = true;
			Loop(j, a.to.size()) {
				node* b = &nodes[a.to[j]];
				if ((*b).done) continue;
				if (a.cost[j] < (*b).d) {
					(*b).d = a.cost[j];
					(*b).from = a.id;
					pq.push(*b);
				}
			}
		}
		Loop(i, n) {
			result[i] = nodes[i].d;
		}
	}
};

int main() {
	int n; cin >> n;
	vector<vector<P>> data(n);
	Loop(i, n) {
		Loop(j, n) {
			int x; cin >> x;
			if (x == -1) continue;
			else data[i].push_back({ j,x });
		}
	}
	MST mst(data);
	mst.mainfunc(0);
	ll ans = 0;
	Loop(i, n) {
		ans += mst.result[i];
	}
	cout << ans << endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
static const int N = 100;
static const int INF = 100000;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, M[N][N];


int prim() {
    int u, minv;
    int color[N], d[N], p[N];
    for (int i = 0; i < n; i++){
        color[i] = WHITE;
        d[i] = INF;
        p[i] = -1;
    }

    d[0] = 0;

    while(true) {
        minv = INF;
        u = -1;
        // Tからの距離がもっとも短いものを次のノードとして選ぶ
        for (int i = 0; i < n; i++) {
            if (minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1) break; // なければ修了
        color[u] = BLACK; // uをT側に取り込む
        // d[]を更新(Tからの距離を更新)
        for (int v = 0; v < n; v++){
            if (color[v] != BLACK && M[u][v] != INF){
                if (M[u][v] < d[v]) {
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    int sum = 0;
    for (int i = 0; i < n; i++) {
        if (p[i] != -1) sum += M[i][p[i]];
    }
    return sum;
}

int main() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int e;
            cin >> e;
            M[i][j] = (e == -1) ? INF : e;
        }
    }

    cout << prim() << endl;

    return 0;
}