Go: package main

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

const (
	MAX = 100
	INF = 1 << 21
	WHITE = 0
	GRAY = 1
	BLACK = 2
)

var (
	n int
	M [MAX][MAX]int
)

func prim() int {
	var u, minv int
	var d [MAX]int
	var p [MAX]int
	var color [MAX]int

	for i := 0; i < n; i++ {
		d[i] = INF
		p[i] = -1
		color[i] = WHITE
	}
	d[0] = 0
	for {
		minv = INF
		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] != INF {
				if d[v] > M[u][v] {
					d[v] = M[u][v]
					p[v] = u
					color[v] = GRAY
				}
			}
		}
	}
	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	n, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < n; i++ {
		for j := 0; j < n; j++ {
			scanner.Scan()
			e, _ := strconv.Atoi(scanner.Text())
			if e == -1 {
				M[i][j] = INF
			} else {
				M[i][j] = e
			}
		}
	}
	fmt.Println(prim())
}

C++: #include <iostream>
#include <algorithm>
using namespace std;
int P[10000];
void init(int N) {
  for (int i = 0; i < N; i++) {
    P[i] = i;
  }
}

int root(int a) {
  if(P[a] == a)
    return a;
  return (P[a] = root(P[a]));
}

bool is_same_set(int a, int b) {
  return root(a) == root(b);
}

void unite(int a, int b) {
  P[root(a)] = root(b);
}

int main()
{
  int N;
  cin >> N;
  int A[N][N];
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
      int x;
      cin >> x;
      A[j][i] = x;
      // cout << "cost: " << x << " = " <<  j << "->"  << i << endl;
    }
  }
  // cout << "-----エッジ-------" << endl;
  int cost[10000], src[10000], dst[10000];
  int M = 0;
  for (int r = 0; r < N; r++)
  {
    for (int c = r + 1; c < N; c++)
    {
      if (A[r][c] > -1)
      {
        cost[M] = A[r][c];
        src[M] = r;
        dst[M] = c;
        // cout << "cost: " << cost[M] << " = " <<  src[M] << "->"  << dst[M] << endl;
        M += 1;
      }
    }
  }
  // cout << "M = " << M << " N = " << N << endl;
  init(N);
  pair<int, pair<int, int> > edges[M + 1];
  for (int m = 0; m < M; m++)
  {
    edges[m] = make_pair(cost[m], make_pair(src[m], dst[m]));
  }
  // cout << "-----sort前-------" << endl;
  // for (int i = 0; i < M; i++)
  //     cout << "cost: " << edges[i].first << " = " << edges[i].second.first << "->"  << edges[i].second.second << endl;
  sort(edges, edges+M);
  // cout << "-----sort後-------" << endl;
  // for (int i = 0; i < M; i++)
  //     cout << "cost: " << edges[i].first << " = " << edges[i].second.first << "->"  << edges[i].second.second << endl;
  int sum = 0;
  for (int i=0; i<M; i++) {
    if (is_same_set(edges[i].second.first, edges[i].second.second))
      continue;
    unite(edges[i].second.first, edges[i].second.second);
    sum += edges[i].first;
  }
  cout << sum << endl;
}

C++: // http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A
// Graph II - Minimum Spanning Tree
// TODO: REVIEW

#define SUBMIT

#include <utility>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <limits>
#include <numeric>
#include <functional>
#include <set>
#include <cmath>
#include <cstring>
#include <climits>
#include <memory>

using namespace std;
using ui64 = unsigned long long;
using i64 = long long;

enum class color_type {
    white,
    gray,
    black
};

const int INF = INT_MAX;
const ui64 MAX_N = 100;
int adj[MAX_N][MAX_N];
int n;

int prim() {
    int d[MAX_N], p[MAX_N];
    color_type color[MAX_N];

    for (int i = 0; i < n; ++i) {
        d[i] = INF;
        p[i] = -1;
        color[i] = color_type::white;
    }

    d[0] = 0;

    while (true) {
        // 未訪問のノード
        int u = -1, min_v = INF;
        for (int i = 0; i < n; ++i) {
            if (d[i] < min_v && color[i] != color_type::black) {
                u = i;
                min_v = d[i];
            }
        }

        if (u == -1) break;

        color[u] = color_type::black;
         for (int v = 0; v < n; ++v) {
            if (color[v] != color_type::black && adj[u][v] != INF) {
                if (adj[u][v] < d[v]) {
                    d[v] = adj[u][v];
                    p[v] = u;
                    color[v] = color_type::gray;
                }
            }
        }
    }

    int sum = 0;
    for (int i = 0; i < n; ++i) {
        if (p[i] != -1) sum += adj[i][p[i]];
    }

    return sum;
}

int main() {
#ifdef SUBMIT
    auto& stream = cin;
#else
    string program_input_str = R"(20
 -1 100 2 -1 5 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 100 -1 3 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 2 3 -1 1 10 12 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 -1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 5 -1 10 -1 -1 2 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 12 -1 2 -1 19 3 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 19 -1 17 -1 -1 3 4 -1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 3 17 -1 5 2 1000 -1 -1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 5 -1 5 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 2 5 -1 1 -1 -1 50 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 3 1000 -1 1 -1 8 100 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 4 -1 -1 -1 8 -1 7 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 100 7 -1 1 5 2 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 50 -1 -1 1 -1 -1 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 5 -1 -1 2 3 -1 3 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 2 -1 2 -1 -1 -1 -1 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 3 -1 -1 5 -1 -1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 5 -1 1 1
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 3 -1 -1 1 -1 3
 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 1 3 -1
)";
    stringstream stream(program_input_str);
#endif
    memset(adj, 0, sizeof(adj));
    stream >> n;

    int w;
    for (int y = 0; y < n; ++y) {
        for (int x = 0; x < n; ++x) {
            stream >> w;
            if (w == -1) adj[y][x] = INF;
            else adj[y][x] = w;
        }
    }

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

C++: n = int(raw_input())
A = [0]
i = 0
long = 0
NY = range(1, n)
a = [[0 for i in xrange(n)] for j in xrange(n)]
while i <=n:
    a[i] = map(int,raw_input().split())
    i = i+1
while NY != []:
    amin = 2001
    for i in A:
        for j in NY:
            if 0 <= a[i][j] < amin:
                amin = a[i][j]
                addA = j
    A.append(addA)
    NY.remove(addA)
    long =long + amin
print long

C++: #include <bits/stdc++.h>
using namespace std;

int n;
vector< vector<int> > a;

int Prim() {
  vector<int> color(n);
  vector<int> d(n, 1000000000);
  vector<int> p(n);
  d[0] = 0, p[0] = -1;

  while (true) {
    int min_cost = 1000000000, u;
    for (int i = 0; i < n; i++) if (color[i] != 2 && d[i] < min_cost) min_cost = d[i], u = i;
    if (min_cost == 1000000000) break;
    color[u] = 2;
    for (int v = 0; v < n; v++)
      if (color[v] != 2 && a[u][v] != -1)
        if (a[u][v] < d[v]) d[v] = a[u][v], p[v] = u, color[v] = 1;
  }

  int ans = 0;
  for (int i = 0; i < n; i++) if(p[i]!=-1 )ans += a[i][p[i]];

  return ans;
}

int main() {
  cin >> n;
  a.resize(n, vector<int>(n));
  for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) cin >> a[i][j];
  cout << Prim() << endl;
}