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>

using namespace std;

static const int MAX = 100;
static const int NIL = (1 << 21);
static const int WHITE = 0;
static const int GREY = 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] = INFY;
    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; i < n; i++) {
      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 <iostream>
#define INF 2000000
#define MAX 100
#define WHITE 0
#define BLACK 1

using namespace std;

int n, d[MAX], color[MAX], w[MAX][MAX];

void prim(int r){
    int u;
    for(u = 0; u < n; u++){
        d[u] = INF;
        color[u] = WHITE;
    }
    d[r] = 0;

    while(1){
        int mincost = INF;
        for(int i = 0; i < n; i++){
            if(color[i] != BLACK && d[i] < mincost){
                mincost = d[i];
                u = i;
            }
        }
        if(mincost == INF) break;
        
        color[u] = BLACK;

        for(int v = 0; v < n; v++){
            if(color[v] != BLACK && w[u][v] < d[v]){
                d[v] = w[u][v];
            }
        }
    }
}

int main(){
    int i, j;
    cin >> n;
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){
            cin >> w[i][j];
            if(w[i][j] == -1) w[i][j] = INF;
        }
    }

    prim(0);

    int sum = 0;
    for(i = 0; i < n; i++){
        sum += d[i];
    }
    cout << sum << endl;
    return 0;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;
int p[101],r[101];
void makeset(int x){
    for(int i=0;i<x;++i){
        p[i]=i;
        r[i]=0;
    }
}
int root(int a){
    if(a!=p[a])
        p[a]=root(p[a]);
    return p[a];
}
bool same(int a,int b){
    return (root(a)==root(b));
}
void link(int a,int b){
    if(r[a]>r[b]){
        p[b]=a;
    }
    else{
        p[a]=b;
        if(r[a]==r[b]){
            r[b]++;
        }
    }
}
void unite(int a,int b){
    link(root(a),root(b));
}
struct Edges{int cost,src,dst;}edges[10010];
bool operator<(const Edges &x,const Edges &y){return x.cost<y.cost;}
int main(){
    int N,M=0;
    int A[101][101];
    cin>>N;
    makeset(N);
    for(int r=0;r<N;++r){
        for(int c=0;c<N;++c){
            cin>>A[r][c];
        }
        for(int c=r+1;c<N;++c){
            if(A[r][c]>-1){
                edges[M].cost=A[r][c];
                edges[M].src=r;
                edges[M].dst=c;
                M+=1;
            }
        }
    }
    sort(edges,edges+M);
    int total=0,num=0,flag=0;
    for(int i=0;i<M;++i){
        if(same(edges[i].src,edges[i].dst)){continue;}
        else{
            unite(edges[i].src,edges[i].dst);
            total+=edges[i].cost;
            num++;
        }
        if(num==N-1){
            flag=1;
            break;
        }
    }
    if(flag){
        cout<<total<<endl;
    }
}

C++: #include <bits/stdc++.h>
#define MOD 1000000007
#define INF 1<<30
#define rep(i,n) for(ll i=0; i<(n); i++)
#define REP(i,a,b) for(ll i=(a); i<(b); i++)
#define RREP(i,a,b) for(ll i=(a); i>=(b); i--)
#define all(x) (x).begin(),(x).end()
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<ll, ll> p;
typedef vector<pair<ll, ll>> vpl;

vvl m(105, vl(105,INF));
ll n;

ll prim(){
    ll u, minv=INF;
    vl visit(105,0);
    vl d(105,INF);
    vl p(105,-1);

    d[0] = 0;
    while(1){
        minv = INF;
        rep(i,n){
            if(d[i] < minv && visit[i] == 0){
                minv = d[i];
                u = i;
            }
        }
        if(minv == INF) break;
        visit[u] = 1;
        rep(i,n){
            if(visit[i] == 0 && m[u][i] != INF){
                if(d[i] > m[u][i]){
                    d[i] = m[u][i];
                    p[i] = u;
                }
            }
        }
    }
    ll sum=0;
    rep(i,n){
        if(p[i] != -1) sum += d[i];
    }
    return sum;
}

int main(){
    ll t;
    cin >> n;
    rep(i,n){
        rep(j,n){
            cin >> t;
            m[i][j] = (t==-1) ? INF : t;
        }
    }

    cout << prim() << "\n";

    return 0;
}

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

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> COL(n, WHITE);
    COL[0] = GRAY;
    int sum = 0;
    while (1) {
        pair<int, int> min_bridge = make_pair(0, 0);
        for (int i = 0; i < n; i++) {
            if (COL[i] != GRAY) continue;
            bool flag = true;
            for (int j = 0; j < n; j++) {
                if (COL[j] != WHITE) continue;
                flag = false;
                if (G[i][j] < G[min_bridge.first][min_bridge.second]) {
                    min_bridge.first  = i;
                    min_bridge.second = j;
                }
            }
            if (flag) COL[i] = BLACK;
        }
        if (min_bridge.first == 0 && min_bridge.second == 0) break;
        COL[min_bridge.second] = GRAY;
        sum += G[min_bridge.first][min_bridge.second];
    }
cout << sum << endl;
    return 0;
}