Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

C++: #include <iostream>
#include <algorithm>
#include <utility>
#include <vector>
#include <queue>
using namespace  std;
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }
struct Edge{
    int from, to, cost;
    Edge(int f, int t, int c){
        from = f;
        to = t;
        cost = c; 
    }
};
bool operator< (const Edge& e1, const Edge& e2){
    return e1.cost < e2.cost;
}
bool operator> (const Edge& e1, const Edge& e2){
    return e1.cost > e2.cost;
}
int makeMST(vector<vector<int>> &G, vector<vector<int>> &H){
    int N = G.size();
    int res = 0;
    int v = 0;
    priority_queue<Edge, vector<Edge>, greater<Edge> > pq;
    vector<int> visited(N, 0);
    visited[0] = 1;
    for(int i=0; i<N; i++) if(G[v][i]!=-1) pq.push(Edge(0, i, G[v][i]));
    int numv = 1;
    while(pq.size() and numv!=N){
        Edge e = pq.top(); pq.pop();
        if(visited[e.to]) continue;
        res += e.cost;
        visited[e.to] = 1;
        H[e.from][e.to] = e.cost;
        H[e.to][e.from] = e.cost;
        for(int i=0; i<N;i++){
            if(G[e.to][i]!=-1 and !visited[i]) pq.push(Edge(e.to, i, G[e.to][i]));
        }
        numv++;
    }
    return res;
}

signed main(){
    int N; cin>>N;
    vector<vector<int>> G(N, vector<int>(N));
    vector<vector<int>> H(N, vector<int>(N, -1));
    for(int i=0; i<N; i++) {
        for(int j=0; j<N; j++){
            cin>>G[i][j];
        }
    }
    cout << makeMST(G, H) << endl;
    return 0;
}

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

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INFTY 1000000


int n,M[100][100],color[100],d[100],p[100];


int prim(){
  int i,u;
  
  for( i = 0; i < 100; i++ ){ 
    color[i] = WHITE;
    d[i] = INFTY;
    p[i] = -1;   
  }

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

    color[u] = BLACK;

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

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

  cout << prim() << endl;

  return 0;
}

C++: #include <iostream>
#include <map>
#include <vector>
using namespace std;
typedef vector <int> vi;
typedef vector <vi> vvi;
struct edge{
	int from;
	int to;
};
typedef multimap <int, edge, less<int> > mme;

int addedge(vvi &graph, int y, int x, int val=1){
	graph[y][x] = val;
	return val;
}

int make_graph(vvi &graph, vi &stamp){
	int n=graph.size(), val;

	for (int j=0; j<n; j++){
		for (int i=0; i<n; i++){
			cin>>val;
			addedge(graph, i, j, val);
		}
		stamp[j] = 0;
	}
	return 0;
}

int Minimum_Spanning_Tree(vvi &graph, vi &stamp){

	mme edges;
	int n = graph.size(), p1, p2, p3, total=0;
	p1=0;
	stamp[p1] = 1;

	while (p1!=-1){
		for (int p2=0; p2<n; p2++){
			int *tmp=&graph[p1][p2];
			if (*tmp!=-1 && stamp[p2]==0){
				edge e;
				e.from = p1;
				e.to = p2;
				edges.insert(pair <int, edge> (*tmp, e));
			}
		}
		p1=-1;
		while (! edges.empty()){
			auto it = edges.begin();
			if (stamp[it->second.from]==1 && stamp[it->second.to]==0){
				p1 = it->second.to;
				stamp[p1]=1;
				total+=it->first;
				edges.erase(it);
				break;
			}
			edges.erase(it);
		}
	}
	return total;
}

int resultout(vvi &graph){
	for (int i=0; i<int(graph.size()); i++){
		for (int j=0; j<int(graph.size()); j++){
		cout<<graph[i][j]<<" ";
		}
		cout<<endl;
	}
	return 0;
}

int main(void){

	int n, row;
	cin>>n;
	vvi G(n, vi(n));
	vi stamp(n);

	make_graph(G, stamp);

	cout<<Minimum_Spanning_Tree(G, stamp)<<endl;

	return 0;
}

C++: #include<iostream>
#include<cstdio>
#define W 0
#define G 1
#define B 2
#define inf 5000
#define MAX 100
#define NIL -1
using namespace std;

int n;
int A[MAX][MAX];

int Prim(){
    int color[MAX],d[MAX],p[MAX];
    int min,u,sum = 0;
    for(int i = 0; i < n; i++){
        color[i] = W;
        d[i] = inf;
        p[i] = NIL;
    }
    
    d[0] = 0;
    
    while(1){
        u = -1;
        min = inf;
        for(int i = 0; i < n; i++){
            if(d[i] < min && color[i] != B){
                u = i;
                min = d[i];
            }
        }
        
        if(u == -1) break;
            
        color[u] = B;
            
        for(int i = 0; i < n; i++){
            if(color[i] != B && A[u][i] != NIL){
                if(A[u][i] < d[i]){
                    d[i] = A[u][i];
                    color[i] = G;
                    p[i] = u;
                }
            }
        }
    }
    
    for(int i = 0; i < n; i++) {
        
        if(p[i] != -1) sum += A[i][p[i]];
        
    }
    
    return sum;
     
}

int main(){
    int x;
    scanf("%d",&n);
    for(int i = 0; i < n; i ++){
        for(int j = 0; j < n; j++){
            scanf("%d",&x);
            if( x == -1) A[i][j] = NIL;
            else A[i][j] = x; 
        }
    }
    
    cout << Prim() << endl;
    return 0;
}