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 <algorithm>
#include <cstdint>

using namespace std;

enum status_t {
  WHITE,
  GRAY,
  BLACK,
};

#define GRAPH_SIZE 101

static uint32_t graph[GRAPH_SIZE][GRAPH_SIZE];
static status_t state[GRAPH_SIZE];
static uint32_t shortest_path[GRAPH_SIZE];

size_t minimum_spanning_tree(size_t num)
{
  size_t minimum_cost = 0;

  while (true) {
    uint32_t minimum = UINT32_MAX;
    uint32_t to = 0;
    for (uint32_t j = 0; j < num; j++) {
      if ((shortest_path[j] < minimum) && state[j] != BLACK) {
        minimum = shortest_path[j];
        to = j;
      }
    }

    if (minimum == UINT32_MAX) break;

    state[to] = BLACK;
    minimum_cost += minimum;

    for (uint32_t j = 0; j < num; j++) {
      if (state[j] != BLACK) {
        shortest_path[j] = min(shortest_path[j], graph[to][j]);
      }
    }
  }

  return minimum_cost;
}

#include <iostream>

int32_t main()
{
  uint32_t num;
  cin >> num;

  for (uint32_t i = 0; i < num; i++) {
    for (uint32_t j = 0; j < num; j++) {
      int32_t val;
      cin >> val;
      if (val == -1) {
        graph[i][j] = UINT32_MAX;
      } else {
        graph[i][j] = val;
      }
    }
  }

  cout << minimum_spanning_tree(num) << endl;

  return 0;
}

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

class DisjointSet {
private:
	vector<int> P;		//添え字の番号の頂点の親
	vector< unordered_set<int> > Set;		//添え字の番号の頂点に子として繋がっている頂点の集合
public:
	DisjointSet(int n);
	void unite(int x, int y);
	bool same(int x, int y);
};

DisjointSet::DisjointSet(int n) : P(n), Set(n) {
	for (int i = 0; i<n; ++i) {
		P[i] = i;
		Set[i].insert(i);
	}
}

void DisjointSet::unite(int x, int y) {
	if (P[x] == P[y])
		return;
	int big, small;
	if (Set[P[x]].size() >= Set[P[y]].size()) {
		big = P[x];
		small = P[y];
	}
	else {
		big = P[y];
		small = P[x];
	}
	for (auto i = Set[small].begin(); i != Set[small].end(); ++i) {
		P[*i] = big;
		Set[big].insert(*i);
	}
}

bool DisjointSet::same(int x, int y) {
	return P[x] == P[y];
}

class MSTree : public DisjointSet {
private:
	const int vertex_n;
	vector< pair<int, int> > edge;		//firstは辺の重さ、secondは辺のID(始点・終点)
public:
	MSTree(int n) : DisjointSet(n), vertex_n(n), edge(n*n) {
		for (int i = 0; i < n*n; i++) {
			edge[i].first = -1;
			edge[i].second = i;
		}
	}
	int& GetEdgeWeight(int i, int j) { return edge[vertex_n*i + j].first; }
	int MinEdgeSum();
};

int MSTree::MinEdgeSum() {
	int sum = 0;
	sort(edge.begin(), edge.end());
	for (int i = 0; i < vertex_n*vertex_n; i++) {
		int from = edge[i].second / vertex_n, to = edge[i].second % vertex_n;
		if (edge[i].first == -1 || this->same(from, to))
			continue;
		else {
			this->unite(from, to);
			sum += edge[i].first;
		}
	}
	return sum;
}

int main() {
	int n;
	cin >> n;
	MSTree mst(n);
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> mst.GetEdgeWeight(i, j);
	cout << mst.MinEdgeSum() << endl;
}

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

int n;
int a[101][101];
int flag[101];
int t[101];
int sum = 0;

void prim(){
  int ima = 0;
  int mine = 100000000;
  
  
  for(int k=0;k<n-1;k++) {
    mine = 10000000;
    for(int i=0;i<n;i++) {
      if(flag[i] == 0 && mine > t[i]) {
	mine = t[i];
	ima = i;
      }
    }
    sum += mine;
    flag[ima] = 1;
    
    for(int i=0;i<n;i++) 
      if(a[ima][i] != -1) 
	if(t[i] > a[ima][i] ) t[i] = a[ima][i];
    
    
  }
}

int main() {

  cin >> n;

  for(int i=0;i<n;i++) 
    for(int j=0;j<n;j++) 
      cin >> a[i][j];
  
  for(int i=0;i<n;i++) {
    flag[i] = 0;
    t[i] = 100000000;
  }
  
  t[0] = 0;
  flag[0] = 1;
  for(int i=0;i<n;i++) 
    if(a[0][i] != -1) t[i] = a[0][i];

  prim();

  cout << sum << endl;
 
  return 0; 
  
}

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

struct Edge{
  int weight;
  int to;
  Edge(int w,int t):weight(w),to(t){}
};

const int inf = 1<<28;

bool operator>(Edge e1,Edge e2){
  if(e1.weight != e2.weight) return (e1.weight > e2.weight);
  else return (e1.to > e2.to);
}

int main(){
  int n;
  cin>>n;
  vector<vector<Edge> > Graph(n);
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int temp;
      cin>>temp;
      if(temp != -1){
	Graph[i].push_back(Edge(temp,j));
      }
    }
  }
  priority_queue<Edge,vector<Edge>,greater<Edge> > pq;
  pq.push(Edge(0,0));
  vector<bool> used(n,false);
  vector<int> cost(n,inf);
  int ans = 0;
  while(pq.size()){
    Edge e = pq.top();
    pq.pop();
    if(used[e.to]) continue;
    used[e.to] = true;
    ans += e.weight;
    for(int i=0;i<Graph[e.to].size();i++){
      Edge &edge = Graph[e.to][i]; 
      if(cost[edge.to] > edge.weight){
	cost[edge.to] = edge.weight;
	pq.push(edge);
      }
    }
  }
  cout<<ans<<endl;
  return 0;
}