Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] >= 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A >= edges[j].A })

	sum := 0
	num := 0
	for len(edges) > 0 && num < n-1 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
		num += 1
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

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

#if 0
所用時間: 1h

感想: 思ったより実装すべきコード量が多かった。DisjointSetは今後も使う機会が多そうなので、クラス化してみた。
Pの配列を動的に確保するよう工夫した、良い復習になった。

#endif

int N, buff, M = 0, SUM = 0, A[101][101], cost[5000], dpt[5000], dst[5000];//A[Y][X]
vector<pair<int, int> > edges;

class disjointSet {
private:
    int* P;
    
public:
    disjointSet(){
        P = new int[100000];
    }
    disjointSet(int N){     
        P = new int[N];
    }
    ~disjointSet(){
        delete[] P;
    }

    void init(int N){ //木構造の初期化
        for(int i = 0; i <= N; ++i){
            P[i] = i;
        }
    }

    int root(int a){ //根の参照
        if(P[a] == a) return a;
        return (P[a] = root(P[a]));
    }

    bool is_same_set(int a, int b){ //同じ根か?
        return root(a) == root(b);
    }

    void unite(int a, int b){
        P[root(a)] = root(b); //aのrootをbの子にする
    }
};


void preprocess(){//辺の前処理
  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];
        dpt[M] = r;
        dst[M] = c;
        M++;
      }
    }
  }

  //for(int i = 0; i < M; ++i) cout << cost[i] << endl;

  for(int i = 0; i < M; ++i){
    edges.push_back(make_pair(cost[i], i));
  }
  // for(int i = 0; i < M; ++i) cout << edges[i].first << " " << edges[i].second << endl;

  sort(edges.begin(), edges.end());

  // for(int i = 0; i < M; ++i) cout << edges[i].first << " " << edges[i].second << endl;

}

void solve(){
  disjointSet Union(100000);

  int ans = 0;
  preprocess();

  Union.init(N);

  for(int i = 0; i < M; ++i){
    int index = edges[i].second;
    if(Union.is_same_set(dpt[index], dst[index])) continue;
    else {
      Union.unite(dpt[index], dst[index]);
      // cout << "unite " << dpt[index] << " and " << dst[index] << endl;
      ans += cost[index];
    }
  }
  cout << ans << endl;
}

int main(){

cin >> N;

for(int i = 0; i < N; ++i){
  for(int j = 0; j < N; ++j){
    cin >> buff;
    A[i][j] = buff;
    }
  }

  //行列の表示
  // cout << "Matrix:" << endl;
  // for(int row=0; row < N; ++row){
  //   for(int col = 0; col < N; ++col){
  //     cout << A[row][col];
  //   }
  //   cout << endl;
  // }

  solve();
}

C++: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A

C++: #include <iostream>
#include <vector>
#include <queue>
#define rep(i,n) for(int i=0; i<(n); ++i)
#define fi first
#define se second
using namespace std;
using pii = pair<int, int>;

int N;
int G[101][101];
bool used[101];

int prim()
{
   int sum = 0;
   priority_queue< pii, vector<pii>, greater<pii> > pq;
   pq.push( pii(0, 0) );

   while( !pq.empty() ){
      const pii tmp = pq.top(); pq.pop();
      if( tmp.fi == -1 || used[ tmp.se ]++ )continue;
      sum += tmp.fi;

      rep(i, N)
         pq.push( pii( G[tmp.se][i], i ) );
   }
   return (sum);
}

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

   rep(i, N)rep(j, N){
      cin >> G[i][j];
   }
   cout << prim() << '\n';
}