Go: package main

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

const (
	white int = iota
	gray
	black
)
const INFTY int = 2001

var G [][]int
var color []int
var d []int
var p []int
var N int

func prim() int {
	u := 0
	d[u] = 0
	for {
		minCost := INFTY
		for i:=0; i<N; i++ {
			if color[i] != black && d[i] < minCost {
				minCost = d[i]
				u = i
			}
		}

		if minCost == INFTY {
			break
		}

		color[u] = black

		for v:=0; v<N; v++ {
			if color[v] != black && G[u][v] != -1 {
				if G[u][v] < d[v] {
					d[v] = G[u][v]
					p[v] = u
					color[v] = gray
				}
			}
		}
	}
	// sum
	sum := 0
	for i:=0; i<N; i++ {
		if p[i] != -1 {
			sum += G[i][p[i]]
		}
	}
	return sum
}




func initVariable(N int) {
	G = make([][]int, N)
	for i:=0; i<N; i++ {
		G[i] = make([]int, N)
	}
	color = make([]int, N)
	d = make([]int, N)
	p = make([]int, N)
	for i:=0; i<N; i++ {
		d[i] = INFTY
		p[i] = -1
	}
}

func nextInt(scanner *bufio.Scanner) int {
	scanner.Scan()
	num, _ := strconv.Atoi(scanner.Text())
	return num
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	N = nextInt(scanner)
	initVariable(N)
	for i:=0; i<N; i++ {
		for j:=0; j<N; j++ {
			G[i][j] = nextInt(scanner)
		}
	}
	fmt.Printf("%d\n", prim())
}

C++: #include <stdio.h>
static const int MAX=100;
static const int INFTY=(1<<30);
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,M[MAX][MAX];

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

    for(i=0;i<n;i++){
        d[i]=INFTY;
        p[i]=-1;
        color[i]=WHITE;
    }
    d[0]=0;
    while(1){
        minv=INFTY;
        u=-1;
        for(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(i=0;i<n;i++){
            if(color[i]!=BLACK && M[u][i]!=INFTY){
                if(d[i]>M[u][i]){
                    d[i]=M[u][i];
                    p[i]=u;
                    color[i]=GRAY;
                }
            }
        }
    }
        sum=0;
        for(i=0;i<n;i++)
            if(p[i]!=-1)
                sum+=M[i][p[i]];
    return sum;
}

int main(void){
    int i,o,e;
    scanf("%d",&n);
    for(i=0;i<n;i++)
        for(o=0;o<n;o++){
            scanf("%d",&e);
            M[i][o]=(e==-1)?INFTY:e;
        }
    printf("%d\n",prim());
    return 0;
}

C++: #include<iostream>
#include<utility>
#include<algorithm>
using namespace std;
int matrix[100][100];
pair<int,int> edges[100];
int cost[100];
int src[100];
int dst[100];
int p[10010];
void init(int n)
{
    for(int i=0;i<=n;i++)
        p[i]=i;
};
int root(int a)
{
    if(p[a]==a)
        return a;
    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,amount=0,sum=0;
    
    cin>>n;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>matrix[i][j];
        }
    }
    
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<=i;j++)
        {
            if(matrix[i][j]!=-1)
            {
                cost[amount]=matrix[i][j];
                src[amount]=i;
                dst[amount]=j;
                amount++;
            }
        }
    }
    for(int i=0;i<amount;i++)
    {
        edges[i]=make_pair(cost[i],i);
    }

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

C++: #define dbg(...) fprintf(stderr,__VA_ARGS__)
#define dpr(x) cerr<<#x<<": "<<x<<endl;
#define dprc(c) do{cerr<<#c<<":";for(auto&_i:(c)){cerr<<" "<<_i;}cerr<<endl;}while(0)
#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
int INF = 1e9+7;
#define all(c) (c).begin(), (c).end()
#define tr(i,c) for(auto i=(c).begin();i!=(c).end();i++)
#define rtr(i,c) for(auto i=(c).rbegin();i!=(c).rend();i++)
#define rep(i,b) for(auto i=0;i<(b);i++)
#define pb push_back
#define sz(c) int((c).size())

#define MAX_N 110

class UnionFind {
public:
  UnionFind(size_t s) : parent_(s), rank_(s, 0) {
    for (size_t i = 0; i < s; i++) {
      parent_[i] = i;
    }
  }

  void unite(size_t x, size_t y) {
    size_t xp = find(x);
    size_t yp = find(y);

    if (xp == yp) return;
    if (rank_[xp] < rank_[yp]) {
      parent_[xp] = parent_[yp];
    } else {
      if (rank_[xp] == rank_[yp]) rank_[xp]++;
      parent_[yp] = parent_[xp];
    }
  }

  bool is_same(size_t x, size_t y) {
    return find(x) == find(y);
  }

  size_t find(size_t x) {
    if (parent_[x] == x) return x;
    else return parent_[x] = find(parent_[x]);
  }

  size_t size() const {
    return parent_.size();
  }

private:
  vector<int> parent_;
  vector<int> rank_;
};

struct edge {
  int w, v, u;
};

void printuf(UnionFind& uf) {
  for (int i = 0; i < sz(uf); i++) {
    fprintf(stderr, " %-2d", i);
  }
  puts("");
  for (int i = 0; i < sz(uf); i++) {
    fprintf(stderr, " %-2lu", uf.find(i));
  }
  puts("");
}

int main(int argc, char **argv)
{

  int n;
  scanf("%d", &n);

  vector<edge> E;

  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      int x;
      scanf("%d", &x);
      if (i >= j) continue;
      edge e = {x, i, j};
      if (x >= 0) E.pb(e);
    }
  }

  sort(all(E), [=](const edge& lhs, const edge& rhs) { return lhs.w < rhs.w; });

  UnionFind S(n);

  int total = 0;

  for (int i = 0; i < sz(E); i++) {
    edge& e = E[i];

    int v = S.find(e.v);
    int u = S.find(e.u);

    if (v == u) continue;
    total += e.w;
    S.unite(e.v, e.u);
  }

  printf("%d\n", total);

  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define inf (1 << 30)

static const int N = 100;
static const int white = 0;
static const int gray = 1;
static const int black = 2;

int n;
int m[N][N];

int prim() {
	int color[N];
	int d[N], p[N];
	int u;
	for (int i = 0; i < n; i++) {
		color[i] = white;
		d[i] = inf;
		p[i] = -1;
	}
	//color[0] = black;
	d[0] = 0;
	p[0] = -1;
	u = 0;
	while (true) {
		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) {
				if (m[u][v] < d[v]) {
					d[v] = m[u][v];
					color[v] = gray;
					p[v] = u;
				}
			}
		}
	}
	int sum = 0;
	for (int i = 0; i < n; i++) {
		if (color[i] == black) {
			sum += d[i];
		}
	}
	return sum;
}

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int v;
			cin >> v;
			v == -1 ? m[i][j] = inf : m[i][j] = v;
		}
	}
	prim();
	cout << prim() << endl;
	return 0;
}