Go: package main

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

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

C++: #include <stdio.h>
#define MAX 100
static const int INFTY = (1<<21);
int n,A[MAX][MAX];

int prim();

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

int prim(){
  int e,min,i,v,sum=0;
  int g[MAX],r[MAX],a[MAX];

  for(i=0;i<n;i++){
    g[i]=INFTY;
    r[i]=-1;
    a[i]=0;
  }
  g[0]=0;

  while(1){
    min=INFTY;
    e=-1;
    for(i=0;i<n;i++){
      if(min>g[i]&&a[i]!=2){
	e=i;
	min=g[i];
      }
    }
    if(e==-1)
      break;
    a[e]=2;
    for(v=0;v<n;v++){
      if(a[v]!=2&&A[e][v]!=INFTY){
	if(g[v]>A[e][v]){
	  g[v]=A[e][v];
	  r[v]=e;
	  a[v]=1;
	}
      }
    }
  }
  for(i=0;i<n;i++){
    if(r[i]!=-1)
      sum+=A[i][r[i]];
  }
  return sum;
}

C++: #include <iostream>
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;
static const int MAX = 2000;

int d[110], p[110];
int color[110];

int main() {
  int n;
  std::cin >> n;
  int G[110][110];

  for(int i=0; i<n; ++i) {
    for(int j=0; j<n; ++j) {
      int v;
      std::cin >> v;
      if(v != -1) {
        G[i][j] = v;
      } else {
        G[i][j] = MAX;
      }
    }
  }

  for(int i=0; i<n; ++i) {
    color[i] = WHITE;
    d[i] = MAX;
  }

  d[0] = 0;
  p[0] = 0;

  while(true) {
    int mini_cost = MAX;
    int u;
    // 最小の重みとなる辺を探している
    for(int i=0; i<n; ++i) {
      if(color[i] != BLACK && d[i] < mini_cost) {
        mini_cost = d[i];
        u = i;
      }
    }

    if(mini_cost == MAX) {
      break;
    }

    color[u] = BLACK;

    for(int v=0; v < n; ++v) {
      if(color[v] != BLACK && G[u][v] != MAX) {
        if(G[u][v] < d[v]) {
          d[v] = G[u][v];
          p[v] = u;
          color[v] = GRAY;
        }
      }
    }
  }

  int d_sum = 0;
  for(int i=0; i<n; ++i) {
    d_sum += d[i];
  } 

  std::cout << d_sum << std::endl;
}

C++: #include <iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
const int maxn=111;
const int inf=0x3f3f3f3f;
int e[maxn][maxn];
int n;
int  p[maxn];
int b[maxn];
int vis[maxn];
void prime()
{
    memset(vis,0,sizeof(vis));
    memset(p,-1,sizeof(p));
    for(int i=0; i<n; i++)
        b[i]=inf;
    b[0]=0;
    while(1)
    {
        int ans=inf;
        int v=-1;
        for(int i=0; i<n; i++)
        {
            if(vis[i]==0&&b[i]<ans)
            {
                v=i;
                ans=b[i];
            }
        }
        if(v==-1)
            break;
        vis[v]=1;
        for(int i=0; i<n; i++)
        {
            if(b[i]>e[v][i]&&vis[i]==0)
            {
                b[i]=e[v][i];
                p[i]=v;
                //printf("%d\n",v);
            }
        }
    }
 
    int sum=0;
    for(int i=0;i<n;i++)
    {
        if(p[i]!=-1)
            sum+=e[p[i]][i];
    }
    printf("%d\n",sum);
}
int main()
{
    scanf("%d",&n);
    for(int i=0; i<n; i++)
        for(int j=0; j<n; j++)
        {
            int x;
            scanf("%d",&x);
            if(x==-1)
                e[i][j]=inf;
            else e[i][j]=x;
        }
    prime();
    return 0;
}

C++: #include<iostream>

using namespace std;

static const int MAX = 100;
static const int NIL = (1 << 21);
static const int WHITE = 0;
static const int GREY = 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] = INFY;
    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; i < n; i++) {
      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;
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;
}