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;

#define INF INT32_MAX

int main()
{
	int n;
	cin >> n;
	vector<vector<int>> cost( n, vector<int>( n ) );
	for( int i = 0; i < n; i++ ) {
		for( int j = 0; j < n; j++ ) {
			int c;
			cin >> c;
			cost[i][j] = INF;
			if( c >= 0 ) cost[i][j] = c;
		}
	}

	vector<int> mincost( n, INF );
	vector<int> used( n );
	mincost[0] = 0;
	int ans = 0;
	while( true ) {
		int v = -1;
		for( int u = 0; u < n; u++ ) {
			if( used[u] == 0 && ( v < 0 || mincost[u] < mincost[v] ) ) v = u;
		}
		if( v < 0 ) break;
		used[v] = 1;
		ans += mincost[v];
		for( int u = 0; u < n; u++ ) {
			mincost[u] = min( mincost[u], cost[v][u] );
		}
	}

	cout << ans << endl;
}

C++: #include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <utility>

using namespace std;

#define REP(var, count) for(int var=0; var<count; var++)

struct unionf {
	
	vector<int> data;
	
	unionf(int n) {
		REP(i, n+1) { data.push_back(i); }
	}
	
	int root(int a) {
		if(data[a] == a) { return a; }
		return (data[a] = root(data[a]));
	}
	
	bool issame(int a, int b) {
		return root(a) == root(b);
	}
	
	void unite(int a, int b) {
		data[root(a)] = root(b);
	}

};

int main(void) {
	int N;
	cin >> N;
	
	vector<pair<int, pair<int, int> > > edge;
	
	REP(x, N) {
		REP(y, N) {
			int c;
			cin >> c;
			if ( x <= y ) { continue; }
			if ( c == -1 ) { continue; }
			edge.push_back( make_pair(c, make_pair(x,y)) );
		}
	}
	
	sort(edge.begin(), edge.end());
	
	unionf uf(N);
	
	int cnt = 0;
	int ret = 0;
	
	REP(i, edge.size() ) {
		
		pair<int, int> sd = edge[i].second;
		if ( ! uf.issame( sd.first, sd.second ) ) {
			cnt ++;
			ret += edge[i].first;
			uf.unite(sd.first, sd.second);
			//cout << "joint " << sd.first << " " << sd.second << " -> " << edge[i].first << endl;
		}
		
		if ( cnt == N-1 ) { break; }
	}
	
	cout << ret << endl;
}

C++: #include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

// =======================
// ------ graph ------ //
using Weight = int;
using Flow = int;
struct Edge {
    int src, dst;
    Weight weight;
    Flow cap;
    Edge() : src(0), dst(0), weight(0) { }
    Edge(int s, int d, Weight w) : src(s), dst(d), weight(w) { }
};
bool operator < (const Edge &e, const Edge &f) {
    return e.weight != f.weight ? e.weight < f.weight :
        e.src != f.src ? e.src < f.src : e.dst < f.dst;
}
using Edges = vector<Edge>;
using Graph = vector<Edges>;

void add_edge1(Graph &g, int a, int b, Weight w = 1) {
    g[a].emplace_back(a, b, w);
}

// ------ disjoint set ------ //
struct UnionFind {
    vector<int> data;
    int __size;
    UnionFind(int size) : data(size, -1), __size(size) { }
    bool unionSet(int x, int y) {
        if ((x = root(x)) != (y = root(y))) {
            if (data[y] < data[x]) swap(x, y);  // par -> child とは限らない
            data[x] += data[y]; data[y] = x; __size--;
        }
        return x != y;
    }
    bool findSet(int x, int y) { return root(x) == root(y); }
    int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
    int size(int x) { return -data[root(x)]; }
    int size() { return __size; }
    vector<int> subset_roots() {
        vector<int> roots;
        for (int i = 0; i < data.size(); i++) if (data[i] < 0) roots.push_back(i);
        return roots;
    }
};

// ------ kruskal ------ //
pair<Weight, Edges> kruskal(const Graph &g) {
    UnionFind uf(g.size());
    Edges es;
    for (auto &adj : g) for (auto &e : adj) es.emplace_back(e);
    sort(es.begin(), es.end());
    Weight total = 0;
    Edges T;
    for (auto &e : es) if (uf.unionSet(e.src, e.dst)) {
        T.push_back(e);
        total += e.weight;
    }
    return make_pair(total, T);
}
// =======================

int main() {
    int n; cin >> n;
    Graph G(n);
    for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) {
        int w; cin >> w;
        if (w >= 0) add_edge1(G, i, j, w);
    }
    pair<Weight, Edges> res = kruskal(G);
    cout << res.first << endl;
    return 0;
}

C++: #include<iostream>
using namespace std;

const int MAX = 100;

int count(bool check[MAX], int graph[MAX][MAX], int n,int i) {
	check[i] = true;
	int sum = 0;
	for (int j = 0; j < n; j++) {
		if (graph[i][j] != -1 && check[j] == false) {
			sum += count(check,graph, n, j);
			sum += graph[i][j];
		}
	}
	return sum;
}

int main() {
	int n;
	int g;
	int graph[MAX][MAX];

	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> graph[i][j];
		}
	}

	//?????±???
	for (int m = 0; m < n; m++) {
		//?§????
		for (int b = 0; b < n; b++) {
			if (graph[b][m] == -1)continue;
			//??????
			for (int e = 0; e < n; e++) {
				if (graph[m][e] == -1 || graph[b][e] == -1)continue;
				if (graph[b][e] >= graph[b][m] + graph[m][e]) {
					graph[b][e] = -1;
				}
			}
		}
	}

	bool check[MAX] = { false };
	cout << count(check, graph, n, 0) << endl;
	return 0;
}