Go: package main

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

const R = 100000000

var sc = bufio.NewScanner(os.Stdin)

var n int
var A [101][101]int

func nextInt() int {
	sc.Scan()
	i, _ := strconv.Atoi(sc.Text())
	return i
}
func prim() int {
	var u, Minimum, sum int
	var d, p, color [101]int

	for i := 0; i < n; i++ {
		d[i] = R
		p[i] = -1
		color[i] = 0
	}
	d[0] = 0

	for {
		Minimum = R
		u = -1
		for i := 0; i < n; i++ {
			if Minimum > d[i] && color[i] != 2 {
				u = i
				Minimum = d[i]
			}
		}
		if u == -1 {
			break
		}
		color[u] = 2
		for j := 0; j < n; j++ {
			if color[j] != 2 && A[u][j] != R {
				if d[j] > A[u][j] {
					d[j] = A[u][j]
					p[j] = u
					color[j] = 1
				}
			}
		}
	}

	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += A[i][p[i]]
		}
	}
	return sum
}
func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {
		for j := 0; j < n; j++ {
			e := nextInt()
			if e == -1 {
				A[i][j] = R
			} else {
				A[i][j] = e
			}
		}
	}
	fmt.Println(prim())
}

C++: #include<bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i) 
#define PI acos(-1)

using namespace std;
using ll = long long;
using P = pair<int, int>;
using LP = pair<ll, ll>;

struct DisjointSet {
private:
    vector<int> par;
    vector<int> rank;

public:
    DisjointSet(int n) {
        par = vector<int>(n);
        rep(i, n) par[i] = i;
        rank = vector<int>(n);
    }

    int find(int i) {
        if (par[i] == i) return i;
        int p = find(par[i]);
        par[i] = p;
        return p;
    }

    bool joint(int i, int j) {
        int pi = find(i);
        int pj = find(j);
        if (pi == pj) return false;

        if (rank[pi] < rank[pj]) this->par[pi] = pj;
        else if (rank[pj] < rank[pi]) this->par[pj] = pi;
        else {
            this->par[pi] = pj;
            rank[pj]++;
        }
        return true;
    }
};

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    cin>>n;
    priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> q;
    rep(i, n) {
        rep(j, n) {
            int w;
            cin>>w;
            if (w == -1) continue;

            vector<int> v = {w, i, j};
            q.push(v);
        }
    }
    DisjointSet ds(n);
    ll ans = 0;
    while (!q.empty()) {
        vector<int> v = q.top(); q.pop();
        int w = v[0];
        int v1 = v[1];
        int v2 = v[2];
        if (ds.joint(v1, v2)) ans += w;
    }
    cout<<ans<<endl;
}

C++: #include<iostream>
#include<algorithm>
using namespace std;

#define INF 2000

int n;
int cost[110][110], mincost[110];
bool used[110];

int prim(){

  //initialization
  for(int i = 0;i < n;i++){
    mincost[i] = INF;
    used[i] = false;
  }

  //cost of starting position is 0
  mincost[0] = 0;
  int ans = 0;
  
  while(true){
    int v = -1;
    
    for(int u = 0;u < n;u++){
      if(!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
    }

    if(v == -1) break; //finish
    used[v] = true; //use v
    ans += mincost[v];

    //update mincost
    for(int u = 0;u < n;u++){
      mincost[u] = min(mincost[u], cost[v][u]);
    }
  }
  
  return ans;
}

int main(){

  //input
  cin >> n;
  for(int i = 0;i < n;i++){
    for(int j = 0;j < n;j++){
      cin >> cost[i][j];
      if(cost[i][j] == -1) cost[i][j] = INF;
    }
  }

  //output
  cout << prim() << endl;
  
  return 0;
}

C++: #include<iostream>
#include<queue>
using namespace std;

const int MAX = 100;

struct Edge {
	Edge(int v1, int v2, int cost) :v1(v1), v2(v2), cost(cost) {};
	bool operator < (const Edge& e) const {
		return cost > e.cost;
	}
	int v1;
	int v2;
	int cost;
};

int parent(int uft[], int c) {
	if (uft[c] == -1)return c;
	return uft[c] = parent(uft, uft[c]);
}

int main() {
	int n;
	int uft[MAX];
	int sum = 0;
	priority_queue<Edge> q;
	
	cin >> n;

	for (int i = 0; i < n; i++) {
		uft[i] = -1;
	}

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int temp;
			cin >> temp;
			if (temp != -1){
				Edge e(i, j, temp);
				q.push(e);
			}
		}
	}

	while (!q.empty()) {
		Edge e = q.top(); q.pop();
		int p1 = parent(uft, e.v1);
		int p2 = parent(uft, e.v2);

		if (p1 != p2) {
			uft[p1] = p2;
			sum += e.cost;
		}
	}

	cout << sum << endl;
}

C++: #include<iostream>
#define MAX 101
#define INF (2<<29)
using namespace std;
int main(){
  int n;
  cin>>n;
  int graph[MAX][MAX];
  
  for(int i=1;i<n+1;i++){
    for(int j=1;j<n+1;j++){
      cin>>graph[i][j];
      if(graph[i][j]==-1)graph[i][j]=INF;
    }
  }
  
  int visited[MAX];
  int min[MAX];
  for(int i=1;i<n+1;i++){
    visited[i]=0;
    min[i]=INF;
  }
  
  min[1]=0;
  int ans=0;
  while(true){
    int a=-1;
    for(int i=1;i<n+1;i++){
      if(visited[i]==0&&(a==-1||min[i]<min[a]))a=i;
    }

    if(a==-1)break;
    visited[a]=1;
    ans +=min[a];

    for(int i=1;i<n+1;i++){
      min[i]=min[i]<graph[a][i] ? min[i]:graph[a][i];
    }
  }
  cout<<ans<<endl;
  return 0;
}

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

struct edge {
	int x;
	int y;
	int cost;
	edge(int x, int y, int cost) { this->x = x; this->y = y; this->cost = cost; }
};

bool operator<(const edge& e, const edge& f) { return e.cost < f.cost; }
bool operator<=(const edge& e, const edge& f) { return e.cost <= f.cost; }
bool operator>(const edge& e, const edge& f) { return e.cost > f.cost; }
bool operator>=(const edge& e, const edge& f) { return e.cost >= f.cost; }
bool operator==(const edge& e, const edge& f) { return e.cost == f.cost; }
bool operator!=(const edge& e, const edge& f) { return e.cost != f.cost; }

int root(int* par, int x)
{
	if (par[x] == x) return x;
	else return root(par, par[x]);
}
	
bool isSame(int* par, int x, int y)
{
	return root(par, x) == root(par, y);
}

void unite(int* par, int x, int y)
{
	if (!isSame(par, x, y)) par[root(par, x)] = root(par, y);
}

int main()
{
	int n; std::cin >> n;
	
	int *par = new int[n];
	for (int i=0; i<n; i++) par[i] = i;
	
	std::vector<edge> edge_list;
	
	for (int i=0; i<n; i++) {
		for (int j=0; j<n; j++) {
			int cost;
			std::cin >> cost;
			if (i < j && cost >= 0) edge_list.push_back( edge(i, j, cost) );
		}
	}
	
	std::sort(edge_list.begin(), edge_list.end());
	
	int totalcost = 0;
	int num_of_edges = 0;
	for (std::vector<edge>::iterator it = edge_list.begin(); it != edge_list.end(); ++it) {
		if (isSame(par, (*it).x, (*it).y)) continue;
		unite(par, (*it).x, (*it).y);
		totalcost += (*it).cost;
		num_of_edges++;
		// std::cout << (*it).x << "," << (*it).y << " " << (*it).cost << std::endl;
		if (num_of_edges == n-1) break;
	}
	
	std::cout << totalcost << std::endl;

	delete[] par;
	
	return 0;
}

C++: #include<stdio.h>
static const int INFTY = (1<<21);
#define MAX 100
#define WHITE 0
#define GRAY 1
#define BLACK 2


int n,v,i,M[MAX][MAX];
int prim(void);

int main(){
  int j,e;
  scanf("%d",&n);

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

int prim(){
  int u,minv,sum=0;
  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(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;
        }
      }
    }
  }
  for(i=0;i<n;i++){
    if(p[i]!=-1)sum+=M[i][p[i]];
  }
  return sum;
}