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>
using namespace std;
static const int MAX=100;
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;
static const int INF=1<<21;

int n;
int A[MAX][MAX];

int prim(){
  int i,color[MAX],d[MAX],p[MAX],mincost,k,sum;
  for(i=0;i<n;i++){
    color[i]=WHITE;
    d[i]=INF;
  }
  d[0]=0;
  p[0]=-1;

  while(1){
    mincost=INF;
    for(i=0;i<n;i++){
      if(color[i]!=BLACK && d[i]<mincost){
	mincost=d[i];
	k=i;
      }
    }
    if(mincost==INF) break;
    color[k]=BLACK;
    for(i=0;i<n;i++){
      if(color[i]!=BLACK && A[k][i]!=INF){
	if(A[k][i]<d[i]){
	  d[i]=A[k][i];
	  p[i]=k;
	  color[i]=GRAY;
	}
      }
    }
  }
  sum=0;
  for(i=0;i<n;i++){
    if(p[i]!=-1){
      sum+=A[i][p[i]];
    }
  }
  return sum;
}

int main(){
  int i,j,a;
  cin>>n;

  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      cin>>a;
      if(a!=-1){
	A[i][j]=a;
      }
      else A[i][j]=INF;
    }
  }

  cout<<prim()<<endl;

  return 0;
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFINITY = (1<<21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int M[MAX][MAX];
int n;

int prim(){
    int u, minv;
    int d[MAX], p[MAX], color[MAX];

    for(int i = 0; i < n; i ++){
        d[i] = INFINITY;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[0] = 0;

    while(1){

        // for(int i = 0; i < n; i++){ //for check
        //     printf("%d ", d[i]);
        // }

        // printf("\n");

        minv = INFINITY;
        u = -1;
        for (int i = 0; i < n; i++){
            if (minv > d[i] && color[i] != BLACK){
                u = i;
                minv = d[i];
            }
        }

        if (u == -1){
            break; //全てのノードが確定している場合、探索終了
        }

        color[u] = BLACK;

        for(int v = 0; v < n; v++){
            if (color[v] != BLACK && M[u][v] != INFINITY){
                if (d[v] > M[u][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(void){
    cin >> n;

    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            int e;
            cin >> e;
            if (e != -1){ 
                M[i][j] = e;
            }else{
                M[i][j] = INFINITY; //無限大を挿入
            }
        }
    }

    cout << prim() << endl;

    return 0;

}

/*
5
-1 2 3 1 -1
2 -1 -1 4 -1
3 -1 -1 1 1
1 4 1 -1 3
-1 -1 1 3 -1
 */

C++: #include<iostream>
#include<queue>
#include<map>
using namespace std;
typedef pair< int, int > Pi;
int info[100][100];
bool used[100];

int prim(const int& V) {
    priority_queue< Pi > que;
    que.push(Pi());
    int ret = 0;
    while (!que.empty()) {
        Pi p = que.top(); que.pop();
        if (!~- p.first || used[p.second]++) continue;
        ret -= p.first;
        for (int i = 0; i < V; i++) que.push(Pi(-info[p.second][i], i));
    }
    return ret;
}

int main() {
    int N;
    cin >> N;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            cin >> info[i][j];
        }
    }
    cout << prim(N) << endl;
}

C++: //kruskal tree
#include <iostream>
#include <algorithm>
using namespace std;
#define M 9999
int parent[M],a[M],b[M];
pair<int,int>node[M];
int root(int a){return parent[a]==a?a:parent[a]=root(parent[a]);}
int unite(int a,int b){
	int x=root(a),y=root(b);
	if(x==y)return 0;
	parent[x]=y;
	return 1;
}
int main(){
	int i,j,s,n,m,x;
	cin>>n;
	for(m=i=0;i<n;i++)for(j=0;j<n;j++)if(cin>>x,~x)a[m]=i,b[m]=j,node[m].first=x,node[m].second=m++;
	sort(node,node+m);
	for(i=0;i<n;i++)parent[i]=i;
	for(s=i=0;i<m;i++)if(unite(a[node[i].second],b[node[i].second]))s+=node[i].first;
	cout<<s<<endl;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
//#include "MyMath.h"
//#include "MyDisjointset.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <functional>
#include <stdio.h>
using namespace std;
typedef pair<int, int> P;
const int INF = 2000000000;
int main() {
	int n; cin >> n;
	int m[101][101];
	for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)
		cin >> m[i][j];
	int res = 0;
	int *d = new int[n];
	fill(d, d + n, INF); 
	d[0] = 0;
	bool *visit = new bool [n];
	priority_queue <P, vector<P>, greater<P> > q;
	q.push(P(d[0], 0));
	while (!q.empty()) {
		int f = q.top().first, s = q.top().second;
		visit[s] = true;
		res += f;
		q.pop();
		for (int i = 0; i < n; i++)
			if (!visit[i] && m[s][i] != -1 && m[s][i] > d[i]) {
				d[i] = m[s][i];
				q.push(P(d[i], i));
			}
	}
	cout << res << endl;
	delete[] d, visit;
	return 0;
}