Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

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

const int inf=0x3f3f3f3f;
int G[110][110];
int d[110];
bool vis[110];
int n;

void Dijsktra(){
    d[0]=0;
    for(int i=0;i<n;i++){
        int u=-1,minn=inf;
        for(int j=0;j<n;j++){
           // if(d[j]<minn&&vis[j]==false){
           if(d[u]<minn&&vis[u]==false){
                u=j;
                minn=d[j];
            }
        }
        if(u==-1)
            return ;
        vis[u]=true;
        for(int v=0;v<n;v++){
            if(vis[v]==false&&G[u][v]!=-1&&d[u]+G[u][v]<d[v]){
                d[v]=d[u]+G[u][v];
            }
        }
    }
}

int prim(){
    d[0]=0;
    int ans=0;
    for(int i=0;i<n;i++){
        int u=-1,minn=inf;
        for(int j=0;j<n;j++){
           // if(d[j]<minn&&vis[j]==false){
           if(d[j]<minn&&vis[j]==false){
                u=j;
                minn=d[j];
            }
        }
        if(u==-1)
            return -1;
        vis[u]=true;
        ans+=d[u];
        for(int v=0;v<n;v++){
            if(vis[v]==false&&G[u][v]!=-1&&G[u][v]<d[v]){
                d[v]=G[u][v];
            }
        }
    }
    return ans;
}

int main(){
    //fill(G[0],G[0]+110*110,inf);
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            scanf("%d",&G[i][j]);
        }
    }
    //memset(d,0,sizeof(d));
    memset(vis,0,sizeof(vis));
    fill(d,d+110,inf);
    printf("%d\n",prim());

    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;
}

C++: #if 0
????????£????????????1.5h
??¢?????????????????§??????????????¢??°????????£????????????sum????¨??????¨????????????????????£????????§?????????
???????????¢??????????????§????????????????????????????????????"-1"???????????????????????????????????§?°???????????????????
#endif

#include <iostream>
#include <algorithm>
#include <utility>
using namespace std;

int P[10000+10];

void init(int N){
	for(int i=0;i<=N;++i) P[i]=i;
}
int root(int a){
	if(P[a]==a)return a;
	else return(P[a]=root(P[a]));
}
bool is_same_set(int a,int b){
	return root(a)==root(b);
}
void unite(int a,int b){
	P[root(a)]=root(b);
}
int main(){
	int N;
	cin>>N;
	int A[N][N];
	
	for(int i=0; i<N;i++){
		for(int j=0;j<N;j++){
			cin>>A[j][i]; //???????????\???
		}
	}

	int M = 0; 
	int cost[N*N],src[N*N],dst[N*N];
	for (int r=0; r<N;r++)
		for (int c=0; c<r;c++) //r<c???????§?????????????
			if (A[r][c] > -1) {
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				M += 1;
			}
	pair<int,int> edges[100000+10];
	for(int i=0;i<M;i++)
		edges[i]=make_pair(cost[i],i); //first???????????????second???ID
	sort(edges,edges+M);
	
	//for(int i=0;i<M;++i)
		//cout<<edges[i].first<<endl;

	init(N);
	int sum=0;
	for(int i=0;i<M;i++){
		if(is_same_set(src[edges[i].second],dst[edges[i].second])==false){
			unite(src[edges[i].second],dst[edges[i].second]);
			sum+=edges[i].first;
		}
	}
		cout<<sum<<endl;
}

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

using namespace std;

struct edge{
	int u;	//?????????
	int v;	//??°??????
	int cost;	//??????
	//???????????????????????§?????§?°???¢????????????
	bool operator<(const edge& another) const {
			return cost < another.cost;
	}
};

const int MAX_N = 100;
const int MAX_M = 10000;

edge es[MAX_M];
int par[MAX_N];
int rank[MAX_N];

void initial(int n){		//?????????
	for(int i=0;i<n;i++){
		par[i] = i;
		rank[i] = 0;
	}
}

int find(int x){		//??¨??????????±???????
	if(par[x] == x){
		return x;
	}else{
		return par[x] = find(par[x]);
	}
}

void unite(int x,int y){	//x???????????¨??¨y???????????¨?????????
	x = find(x);	//x???????????¨??????????????????x??¨??????
	y = find(y);	//y???????????¨??????????????????y??¨??????
	if(x == y) return;
	if(rank[x] < rank[y]){
		par[x] = y;
	}else{
		par[y] = x;
		if(rank[x] == rank[y])
			rank[x]++;
	}
}

bool same(int x,int y){	//x,y???????????¨???????????§?????????
	return find(x) == find(y);
}

bool comp(const edge& e1,const edge& e2){
	return e1.cost < e2.cost;
}

int kruskal(int n,int m){
	initial(n);
	int res = 0;
	for(int i=0;i<m;i++){
		edge e = es[i];
		if(!same(e.u,e.v)){
			unite(e.u,e.v);
			res += e.cost;
		}
	}
	return res;
}

int main(){
	int n,m=0,k,l,x;
	cin >> n;	//????????°?????\???
	int cnt=0;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin >> x;
			if(x != -1){
				edge e;
				e.u = i; e.v = j; e.cost = x;
				es[m] = e;
				m++;
			}
		}
	}
	sort(es,es+m);
	cout << kruskal(n,m) << "\n";
}

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

template<class E>
using nega_queue=priority_queue<E,vector<E>,greater<E>>;

UL N;
UL UF[100];
void unite(UL a,UL b){
 a=UF[a]; b=UF[b];
 rep(i,N) if(UF[i]==b) UF[i]=a;
}

int main() {
 scanf("%u",&N);
 nega_queue<pair<int,pair<UL,UL>>> G;
 rep(i,N) rep(j,N){
  int d; scanf("%d",&d);
  if(d!=-1) G.push({d,{i,j}});
 }
 int ans=0;
 rep(i,N) UF[i]=i;
 while(G.size()){
  int d=G.top().first;
  UL u=G.top().second.first;
  UL v=G.top().second.second;
  G.pop();
  if(UF[u]==UF[v]) continue;
  unite(u,v);
  ans+=d;
 }
 printf("%d\n",ans);
 return 0;
}