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++: /*
 * Problem Description: Graph II - Minimum Spanning Tree
 * Category: Graph
 * Author: Khan
 * Date: 22th October, 2017
 */

#include <iostream>

using namespace std;

static const int MAX = 1000;
static const int INF = (1 << 21);
static const int WHITE = 0;
static const int GRAY = 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] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[0] = 0;

    while(true)
    {
        minv = INF;
        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; v < n; ++v)
        {
            if(color[v] != BLACK && M[u][v] != INF)
            {
                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(int argc, char const *argv[])
{
    //freopen("sample.txt", "r", stdin);
    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) ? INF : e;
        }
    }
    cout << prim() << endl;
    return 0;
}

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

int main()
{
	int n, s = 0, rmin, imin;
	int a[100][100];
	int b[100];

	cin >> n;

	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> a[i][j];

	for (int i = 0; i < n; i++)
			b[i] = -1;

	b[0] = 0;
	int ct = 0;

	while (ct < n - 1) {
		imin = 0;
		rmin = 10000;
		for (int j = 0; j < n; j++) {
			if (b[j] > -1) {
				for (int i = 1; i < n; i++) {
					if (a[j][i] > -1 && b[i] < 0 && rmin > a[j][i]) {
						rmin = a[j][i];
						imin = i;
					}
				}
			}
		}
		b[imin] = rmin;
		ct++;
	}

	for (int i = 0; i < n; i++)
		s += b[i];

	cout << s << endl;

	return 0;
}

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

int n, M[100][100];

int prim(){
    int u, minv, d[100], p[100], c[100];
    
    for(int i = 0; i < n; i++){
        d[i] = (1<<21);
        p[i] = -1;
        c[i] = 0;
    }
    d[0] = 0;
    
    while(true){
        minv = (1<<21);
        u = -1;
        for(int i = 0; i < n; i++){
            if(minv > d[i] && c[i] != 2){
                u = i;
                minv = d[i];
            }
        }
        if(u == -1) break;
        c[u] = 2;
        for(int v = 0; v < n; v++){
            if(c[v] != 2 && M[u][v] != (1<<21)){
                if(d[v] > M[u][v]){
                    d[v] = M[u][v];
                    p[v] = u;
                    c[v] = 1;
                }
            }
        }
    }
    int sum = 0;
    for(int i = 0; i < n; i++){
        if(p[i] != -1) sum = 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;
            if(e == -1) M[i][j] = (1<<21);
            else M[i][j] = e;
        }
    }
    cout << prim() << endl;
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
static const int MAX=100;
static const int INFTY=(1<<21);
static const int WHITE=0;
static const int GRAY=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]=INFTY;
		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; 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;
				}
			}
		}
	}
	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>
using namespace std;
#define MAX 100
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,d[MAX+10],p[MAX+10],color[MAX+10];
int W[MAX+10][MAX+10];

int prim()
{
  int v,k,mini,flag,u=0;
  for(int i=0;i<n;i++)
  {
      d[i]=INT_MAX;
      p[i]=-1;
  }
  d[0]=0;
  while(1)
  {
      mini=INT_MAX;
      flag=1;
      for(int i=0;i<n;i++)
      {
          if(d[i]<mini&&color[i]!=BLACK)
          {
              u=i;
              mini=d[i];
              flag=0;
          }
      }
      if(flag) break;
      color[u]=BLACK;
      for(v=0;v<n;v++)
      {
          if(W[u][v]!=INT_MAX&&color[v]!=BLACK)
          {
            if(d[v]>W[u][v])
            {
              d[v]=W[u][v];//更新当前点到最小生成树的距离
              p[v]=u;//每一轮都需要跑更新前驱结点
            }
          }
      }
  }
  int sum=0;
  for(int i=0;i<n;i++)
  {
      if(p[i]!=-1) sum+=W[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;
         W[i][j]=(e==-1)?INT_MAX:e;
        }
        color[i]=WHITE;
    }
    cout<<prim()<<endl;
}