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 <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)   FOR(i,0,n)
#define pb emplace_back
typedef long long ll;
typedef pair<int,int> pint;

const int MAX_N=101;
struct edge{
    int src,dst,cost;
    edge(int src,int dst,int cost):
    src(src),dst(dst),cost(cost){}
    };
bool operator < (const edge &m,const edge &f){
    return m.cost!=f.cost?m.cost<f.cost:
    m.src!=f.src?m.src<f.src:m.dst<f.dst;
}
struct UnionFind{
    int par[MAX_N],rank[MAX_N]; 
    void init(int n){
        for (int i=0;i<n;i++){par[i]=i;rank[i]=0;}
    } 
    int find(int x){
        if (x==par[x]) return (x);
        return (par[x]=find(par[x]));
    }
    void unite(int x, int y){
        x=find(x);y=find(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){return (find(x) == find(y));} 
};
vector<edge> ve;
int n;
int kruskal(){
    sort(ve.begin(),ve.end());
    UnionFind uf;
    uf.init(n);
    int res=0;
    rep(i,ve.size()){
        edge m=ve[i];
        if(!uf.same(m.src,m.dst)){
            uf.unite(m.src,m.dst);
            res +=m.cost;
        }
    }
    return res;
}
int main(){
    cin>>n;
    int a;
    rep(i,n){
        rep(j,n){
            cin>>a;
            if(a!=-1) ve.pb(edge(i,j,a));
        }
    }
    cout<<kruskal()<<endl;
    return 0;
}

C++: #include<iostream>
#include<vector>
#include<queue>
using namespace std;
enum COLOR{WHITE, BLACK};

struct Edge{
    int w, i, j;
    Edge(int w_, int i_, int j_) : w(w_), i(i_), j(j_) {}
    bool operator< (const Edge& right) const{
        return w > right.w;
    }
};

int main(){
    int n;
    cin >> n;
    vector<vector<int> > G(n, vector<int>(n));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> G[i][j];
            if (G[i][j] == -1) G[i][j] = 1e8;
        }
    }
    vector<COLOR> state(n, WHITE);
    priority_queue<Edge> prim;
    state[0] = BLACK;
    int sum = 0;
    int idx_new_gray = 0;
    for (int i = 1; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (state[j] != WHITE) continue;
            prim.push(Edge(G[idx_new_gray][j], idx_new_gray, j));
        }
        while (state[prim.top().j] == BLACK) prim.pop();
        sum += G[prim.top().i][prim.top().j];
        state[prim.top().j] = BLACK;
        idx_new_gray = prim.top().j;
        prim.pop();
    }
    cout << sum << endl;
    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;

    // 黒以外のやつから最小を探す
    for(int i=0;i<n;i++)
    {
      if(minv>d[i] && color[i] != BLACK)
      {
        u=i;
        minv=d[i];
      }
    }

    // 全部黒だったらループ終了
    if(u==-1)break;

    color[u] = BLACK;

    // u番目とつながるものに値を与える(黒以外)
    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++: #include<cstdio>
#include<vector>
#define N_MAX 105
#define INF 32700
using namespace std;
short adj[N_MAX][N_MAX];
struct Node{
    char parent;//父节点
    short weight;//权值
    bool state;//节点状态
}nodes[N_MAX];
char n;
int solve() {
    int res = 0;
    nodes[0].weight = 0;
    nodes[0].parent = -1;
    nodes[0].state = true;
    char nowParent = 0;
    while(true) {
        for(char j = 0; j < n; j++) {
            if(nodes[j].weight > adj[nowParent][j]&&!nodes[j].state) {
                nodes[j].weight = adj[nowParent][j];
            }
        }
        char minId = n;
        for(char i = 0; i < n; i++) {
            if(!nodes[i].state) {
                if(nodes[i].weight < nodes[minId].weight) {
                    minId = i;
                }
            }
        }
        if(minId == n) break;
        else nodes[minId].state = true;
        nodes[minId].parent=nowParent;
        nowParent=minId;
    }
    for(char i = 0; i < n; i++) {
        res += nodes[i].weight;
    }
    return res;
}

int main(){
    freopen("D:/works/C++200/try132_AOJ_ALDS1_12_A/data.txt", "r", stdin);
    scanf("%d", &n);
    for(char i=0;i<n;i++){
        for(char j=0;j<n;j++){
            scanf("%d", &adj[i][j]);
            if(adj[i][j]==-1) adj[i][j]=INF;
        }
        nodes[i].weight=INF;//初始权值
    }
    nodes[n].weight=INF;
    printf("%d\n", solve());
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define INF (1<<29)

int G[100][100], n;

int prim(){
  int p[100], d[100], c[100];
  int u;

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

  d[0] = 0;

  while(1){
    int minv = INF;
    u = -1;
    for(int i = 0; i < n; i++){
      if(minv > d[i] && c[i] != 2){
        u = i;
        // cout << u << endl;
        minv = d[i];
      }
    }

    if(u == -1) break;
    c[u] = 2;
    for(int v = 0; v < n; v++){
      if(c[v] != 2 && G[u][v] != INF){
        if(d[v] > G[u][v]){
          d[v] = G[u][v];
          p[v] = u;
          c[v] = 1;
        }
      }
    }
  }

  int sum = 0;
  for(int i = 0; i < n; i++){
    if(p[i] != -1) sum+=G[i][p[i]];
    // cout << p[i] << endl;
  }
  return sum;
}


  int main(){

    cin >> n;
    for(int i = 0; i < n; i++){
      for(int j = 0; j < n; j++){
        int v;
        cin >> v;
        G[i][j] = v;
        if(v == -1) G[i][j] = INF;
      }
      // cout << endl;
    }

    cout << prim() << endl;

  }