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<stdio.h>
#include<stdlib.h>
#define N 100
#define INF 1000000
#define MIN(a, b) ((a) < (b) ? (a) : (b))

int a[N][N];

typedef struct node{
	int id;
	int cost;
}node;

void swap(node h[],int x,int y){
	node temp=h[x];
	h[x]=h[y];
	h[y]=temp;
	return;
}


void heapsort(node heap[],int num){

	for(int i=num-1;i>0;i--){
		if(i%2==0){
			if(heap[i].cost < heap[i/2-1].cost)swap(heap,i,i/2-1);
		}else {
			if(heap[i].cost < heap[i/2].cost)swap(heap,i,i/2);
		}
	}
	
	return;

}

int update_heap(node heap[],int num){
	int u=heap[0].id;
	swap(heap,0,num-1);
	num--;
	
	for(int i=0;i<num;i++){
		heap[i].cost=MIN(heap[i].cost,a[u][heap[i].id]);
	}
	
	return num;
}




int main(){
	int i,j,n;
	int num=0;/*heapの要素の個数*/
	int ans=0;
	node heap[N];
	
	
	scanf("%d",&n);
	
	
	/*隣接行列の読み込み*/
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
			scanf("%d",&a[i][j]);
			if(a[i][j]==-1)a[i][j]=INF;
		}
	}
	
	/*0以外の頂点をinsert*/
	for(i=1;i<n;i++){
		heap[num].cost=a[0][i];
		heap[num++].id=i;
	}
	
	/*heapを昇順にソート*/
	heapsort(heap,num);
	
	while(num!=0){
		ans+=heap[0].cost;
		num=update_heap(heap,num);
		heapsort(heap,num);
	}
	
	printf("%d\n",ans);
	
	return 0;
	
}

C++: #include<iostream>
#include<cstdio>
#define INF 1000000
#define NIL -2
#define GRAY -3
#define WHITE -4
#define BRACK -5

using namespace std;

int n;
int M[101][101];
int d[101];//重み
int p[101];//親
int color[101];
int sum = 0;

void Prim(int u) {
	color[u] = BRACK;

	for (int i = 1; i <= n; i++) {
		if (color[i] != BRACK && M[u][i] != -1) {
			color[i] = GRAY;
			if (d[i] > M[u][i]) {
				d[i] = M[u][i];
				p[i] = u;
			}
		}
	}

	sum += d[u];

	//全体のうち重みが一番小さいものについて再帰
	//color[v] = WHITE かつ　d[v]が一番小さい点v について再帰
	//かつGRAYの点とつながっている
	int min = 0;
	d[min] = 100000;


	for (int v = 1; v <= n; v++) {
		if (color[v] == GRAY) {
			if (d[v] < d[min]) {
				min = v;
			}
		}
	}

	if (min != 0) {
		Prim(min);
	}
}

int main() {
	cin >> n;

	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			M[i][j] = 0;
		}
	}
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			cin >> M[i][j];
		}
	}
	for (int i = 1; i <= n; i++) {
		color[i] = WHITE;
	}

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

	//関数
	Prim(1);

	cout << sum << endl;


	return 0;
}

C++: #include <stdio.h>

#define NMAX 100
#define WMAX 2000
#define INF WMAX + 1
#define NIL -1

int n;
int M[NMAX][NMAX];
int d[NMAX]; // distance to mst
int p[NMAX]; // parent
int c[NMAX]; // c[i]=1 if i in mst

int solve() { // find total cost of mst
    for (int i = 0; i < n; i++) {
        c[i] = 0;
        p[i] = NIL;
        d[i] = INF;
    }
    d[0] = 0; // root
    p[0] = NIL;
    int total = 0;
    while (1) {
        // find i s.t d[i] is min
        int mincost = INF;
        int u;
        for (int i = 0; i < n; i++) {
            // if i not in mst and d[i] < mincost
            if (!c[i] && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }

        if (mincost == INF)
            break;

        // printf("include %d to mst!\n", u);
        c[u] = 1; // include u to mst
        total += mincost;

        // update d[i] for M[u][i]!=-1
        for (int i = 0; i < n; i++) {
            if (!c[i] && M[u][i] < d[i]) {
                d[i] = M[u][i];
                p[i] = u;
            }
        }
    }
    return total;
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int w;
            scanf("%d", &w);
            if (w != -1) {
                M[i][j] = w;
            } else {
                M[i][j] = INF;
            }
        }
    }
    printf("%d\n", solve());
    return 0;
}

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

int n, M[MAX][MAX];

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

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

  d[0] = 0;

  while( 1 ){
   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 e; cin >> e;
     M[i][j] = (e == -1) ? INFTY ; e;
   }
  }

  cout << prim() << endl;

  return 0;
}