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 <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <queue>
#include <stack>
using namespace std;
const int maxx=110;
const int infinity=(1<<30);

int A[maxx][maxx];
int d[maxx],p[maxx];//d[i]里面存的是V-T中的点，要加入到T中，选取的最小的权值；
					//d[i]=u;表示的是要把V-T中的点i加入到T中所需要的代价是u；
					//p[v]=u;表示的是V-T中的点v，要和T中的点u连接，即u是v的父节点；
bool flag[maxx];	//用flag来标记这个节点是不是在MST中，true是在T里，false是在V-T里；

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

		for(int i=0;i<maxx;i++) {
			flag[i]=false;
			d[i]=infinity;
			p[i]=-1;
		}
		int sum=0,minv,minj;
		flag[1]=true;
		while(1){
			minv=infinity;
			minj=-1;
			for(int i=1;i<=n;i++){
				if(flag[i]==true){
					for(int j=1;j<=n;j++){
						if(A[i][j]!=-1 && A[i][j]<minv && flag[j]==false) {
							minv=A[i][j];
							minj=j;
						} 
					}
				}
			}
//			cout<<minv<<endl;
//			cout<<minj<<endl;
			if(minv==infinity || minj==-1) break;
			flag[minj]=true;
			sum+=minv;
		}
		
		cout<<sum<<endl;
		return 0;
		
}

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

static const int MAX =100;
static const int INF=(1<<21);
static const int WHITE =0;
static const int GRAY =1;
static const int BRACK =2;

int n,A[MAX][MAX];

int prim(){
  int x,minv,d[MAX],p[MAX],c[MAX];

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

  d[0]=0;
  while(1){
    minv=INF;
    x=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i] && c[i]!=BRACK){
	x=i;
	minv=d[i];
      }
    }
    if(x==-1)break;
    c[x]=BRACK;
    for(int v=0;v<n;v++){
      if(c[v]!=BRACK && A[x][v]!=INF){
	if(d[v]>A[x][v]){
	  d[v]=A[x][v];
	  p[v]=x;
	  c[v]=GRAY;
	}
      }
    }
  }
  int sum=0;
  for(int i=0;i<n;i++){
    if(p[i]!=-1)sum+=A[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;
      A[i][j]=(e==-1)?INF:e;
    }
  }

  cout<<prim()<<endl;
  return 0;
}

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

static const int MAX =100;
static const int INFTY=numeric_limits<int>::max();

typedef enum {
    WHITE,
    GRAY,
    BLACK,
}Color;

int n,M[MAX][MAX];

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

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

    d[0]=0;

    while(true){
        minv=INFTY;
        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;
        color[u]=BLACK;
        for(int v=0;v<n;v++){
            if(color[v]!=BLACK&&M[u][v]!=INFTY){
                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(){
    cin>>n;

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

    cout<<Prim()<<endl;

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)

int n;
vector<vector<int>> a(100,vector<int>(100, -1));
vector<int> t, d(100, -1);

void prim(int start) {
    t.push_back(start);
    d[start] = 0;
    while (t.size() < n) {
        int min_v = 2001, min_i;
        rep(i, t.size()) {
            rep(j, n) {
                if (a[t[i]][j] != -1 && d[j] == -1 && a[t[i]][j] < min_v) {
                    min_v = a[t[i]][j];
                    min_i = j;
                }
            }
        }
        t.push_back(min_i);
        d[min_i] = min_v;
    }
    
}

int main() {
    scanf("%d", &n);
    rep(i, n) {
        rep(j, n) {
            scanf("%d", &a[i][j]);
        }
    }
    prim(0);
    int sum = 0;
    rep(i, n) {
        sum += d[i];
    }
    printf("%d\n", sum);
}

C++: #include<iostream>
#define INF 1<<30
using namespace std;
int main() {
  int n; cin >> n;
  int graph[101][101] = {};
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j) cin >> graph[i][j];
  int mincost[101], flag[101] = {}, sum = 0;
  for (int i = 2; i <= n; ++i) mincost[i] = INF;
  mincost[1] = 0;
  while (1) {
    int v = -1;
    for (int i = 1; i <= n; ++i) 
      if (!flag[i] && (v == -1 || mincost[v] > mincost[i])) v = i;
    if (v == -1) break;
    flag[v] = 1;
    sum += mincost[v];
    for (int i = 1; i <= n; ++i)
      if (graph[v][i] != -1 && mincost[i] > graph[v][i]) mincost[i] = graph[v][i];
  }
  cout << sum << endl;
  return 0;
}