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<cstdio>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;

#define INF 20000000
typedef struct Edge edge;

struct Edge{
  int src,dst,weight;
  Edge(int start,int end,int cost) : src(start),dst(end),weight(cost) {}
};

typedef vector<edge> Edges;

bool operator < (const edge &e,const edge &f){
  return (e.weight != f.weight) ? (e.weight > f.weight) : (e.src != f.src) ? (e.src < f.src) : (e.dst < f.dst);
}

class UnionFind{
public:
  int par[1001];
  int rank[1001];

  UnionFind(){
	for(int i = 0;i < 1001;i++){
	  par[i] = i;
	  rank[i] =1;
	}
  }

  int root(int);
  bool findset(int,int);
  void unionset(int,int);
};

void kruskal(Edges);

int main(int argc,char* argv[]){
  int V;
  Edges es;
  int dist;

  cin >> V;
  for(int i = 0;i < V;i++){
	for(int j = 0;j < V;j++){
	  cin >> dist;
	  if(dist != -1){
		edge e(i,j,dist);
		es.push_back(e);
	  }
	}
  }

  kruskal(es);
  return 0;
}

void kruskal(Edges es){
  priority_queue<edge> que;
  int cost = 0;
  UnionFind uf;
  for(int i = 0;i < (int)es.size();i++)
	que.push(es[i]);

  while(!que.empty()){
	edge e = que.top();que.pop();

	if(!uf.findset(e.src,e.dst)){
	  uf.unionset(e.src,e.dst);
	  cost += e.weight;
	}
  }

  printf("%d\n",cost);
}


int UnionFind::root(int x){
  return (par[x] == x) ? x : root(par[x]);
}

bool UnionFind::findset(int x,int y){
  return root(x) == root(y);
}

void UnionFind::unionset(int x,int y){
  x = root(x);
  y = root(y);

  if(x == y)
	return;

  if(rank[y] < rank[x])
	swap(x,y);
  par[y] = x;
  rank[x] += rank[y];
}

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

using namespace std;
const int INF = 1001001001;

int prim(vector< vector<int> > cost)
{
    vector<int> V(1, 0), T(cost.size());
    for(int i=0;i<cost.size();++i) T[i] = i;
    T[0] = INF;
    int mini, minj, min_cost, ans=0;
    while(V.size() < cost.size())
    {
        min_cost = INF;
        for(int i : V){
            for(int j : T)
            {
                if(j == INF) continue;
                if(cost[i][j] < min_cost)
                {
                    mini = i;
                    minj = j;
                    min_cost = cost[i][j];
                }
            }
        }
        V.push_back(minj);
        T[minj] = INF;
        cost[mini][minj] = cost[minj][mini] = INF;
        ans += min_cost;
    }
    return ans;
}

int main()
{
    int n;
    cin >> n;
    vector<vector<int> > cost(n, vector<int>(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;
        }
    }

    cout << prim(cost) << endl;
}

C++: #include <stdio.h>

int n,M[110][110];

int minimum(){
  int color[110],d[110],p[110];
  int i=0,s=0;
  int mincost,v,u;
  while(i<=n){color[i]=0;d[i]=5000;p[i]=-1;i++;}
  d[0]=0;
  while(1){
    mincost = 5000;
    for(i=0;i<n;i++){
      if(color[i] != 2 && d[i]<mincost){
	mincost = d[i];
	u=i;
      }
    }
    if(mincost == 5000){
      break;
    }
    color[u] = 2;
    for(v=0;v<n;v++){
      if(color[v] != 2 && M[u][v]<d[v] && M[u][v]!=-1){
	d[v] = M[u][v];
	p[v] = u;
	color[v] = 1;
      }
    }
  }
  for(i=0;i<n;i++){
    if(d[i]!=5000) s+=d[i];
  }
  return s;
}
int main(void){
  int i,j;
  scanf("%d",&n);
  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      scanf("%d",&M[i][j]);
    }
  }
  printf("%d\n",minimum());
  return 0;
}

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

int x[10000][10000];
int MIN[10000];
int MINX = 0;
int MINZ = 0;

int main() {
	memset(MIN, 127, sizeof(MIN));
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
	for(int h=0;h<n;h++){
		memset(MIN, 127, sizeof(MIN));
		MIN[h] = 0;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				for (int k = 0; k < n; k++) {
					if (x[j][k] != -1) {
						MIN[k] = min(MIN[k], x[j][k]);
					}
				}
			}
		}
		for (int i = 0; i < n; i++) {
			MINX += MIN[i];
		}
		MINZ=min(MINZ,MINX);
	}
	cout << MINZ << endl;
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <cstdio>
#include <utility>
#include <string>
#include <cmath>
#include <cstdlib>
#include <cstring>

using namespace std;

typedef uint64_t u64;
typedef int64_t s64;
typedef uint32_t u32;
typedef int32_t s32;
typedef vector<s32> vs32;
typedef vector<u32> vu32;
typedef vector<s64> vs64;
typedef vector<u64> vu64;

const double PI=3.14159265358979323846;

#define MAX(x, y) ((x) < (y) ? (y) : (x))
#define MIN(x, y) ((x) > (y) ? (y) : (x))

#define rep(i, N) for(int i = 0; i < N; ++i)

#define CEIL(x, y) (((x) + (y) - 1) / (y))
#define MOD 1000000007ULL

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

    int n;
    cin >> n;

    int g[n][n];
    int w;
    rep (i, n)
    {
        rep (j, n)
        {
            cin >> w;
            if (w < 0) w = 1e9;
            g[i][j] = w;
        }
    }

    u64 ans = 0;
    vs32 MST;
    vs32 remain(n - 1);
    rep (i, n - 1) remain[i] = i + 1;
    MST.push_back(0);
    while (MST.size() < n)
    {
        w = 1e9;
        int node;
        for (int u : MST)
        {
            rep (j, remain.size())
            {
                int v = remain[j];
                if (w > g[u][v])
                {
                    w = g[u][v];
                    node = j;
                }
            }
        }
        MST.push_back(remain[node]);
        swap(remain[node], remain.back());
        remain.pop_back();
        ans += w;
    }

    cout << ans << "\n";
    return 0;
}