Go: // Find the minimum spanning tree by the Kruskal algorithm
// -------------------------------------------------------
// Kruskal(G):
//     A = ∅
//     foreach v ∈ G.V:
//        MAKE-SET(v)
//     foreach (u, v) in G.E ordered by weight(u, v), increasing:
//         if FIND-SET(u) ≠ FIND-SET(v):
//             A = A ∪ {(u, v)}
//             UNION(u, v)
//     return A
//
// Ref: https://en.wikipedia.org/wiki/Kruskal%27s_algorithm

package main

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

var scanner = bufio.NewScanner(os.Stdin)
var (
	matrix [][]int
)

type Edge struct {
	a, b, cost, added int
}
type ByCost []Edge

var edges ByCost

func (a ByCost) Len() int           { return len(a) }
func (a ByCost) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a ByCost) Less(i, j int) bool { return a[i].cost < a[j].cost }

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		n, _ := strconv.Atoi(buf[0])
		m, _ := strconv.Atoi(buf[1])
		if n == 0 && m == 0 {
			break
		}
		matrix = make([][]int, n)
		for i := range matrix {
			matrix[i] = make([]int, n)
		}
		for i := 0; i < m; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			a, _ := strconv.Atoi(buf_[0])
			b, _ := strconv.Atoi(buf_[1])
			cost, _ := strconv.Atoi(buf_[2])
			matrix[a][b] = cost
			matrix[b][a] = cost
		}
		sum := Kruskal(n)
		fmt.Println(sum)
		if len(edges) > 0 {
			edges = []Edge{}
		}
	}
}

func Kruskal_func(size, edge_num int) int {
	for i := 0; i < size; i++ {
		for j := 0; j < size; j++ {
			if matrix[i][j] > 0 {
				tmp := Edge{i, j, matrix[i][j], 0}
				edges = append(edges, tmp)
			}
		}
	}
	sort.Sort(ByCost(edges))
	UF_Init(edge_num)
	for i := 0; i < edge_num; i++ {
		a := edges[i].a
		b := edges[i].b
		if UF_Find(a) != UF_Find(b) {
			edges[i].added = 1
			UF_Union(UF_Find(a), UF_Find(b))
		}
	}
	sum := 0
	for i := 0; i < edge_num; i++ {
		if edges[i].added != 0 {
			// log.Printf("edge(%d,%d) is added\n", edges[i].a, edges[i].b)
			sum += edges[i].cost
		}
	}
	return sum
}

func Kruskal(size int) int {
	edge_num := 0
	for i := 0; i < size; i++ {
		for j := 0; j < size; j++ {
			if matrix[i][j] > 0 {
				edge_num++
			}
		}
	}
	return Kruskal_func(size, edge_num)
}

/*** Union-Find functions ***/
var UF_Parent []int
var UF_Rank []int

func UF_Init(n int) {
	UF_Parent = make([]int, n)
	UF_Rank = make([]int, n)
	for i := 0; i < n; i++ {
		UF_Parent[i] = i
		UF_Rank[i] = 0
	}
}
func UF_Union(a, b int) {
	if UF_Rank[a] < UF_Rank[b] {
		UF_Parent[a] = b
	} else {
		UF_Parent[b] = a
	}
	if UF_Rank[a] == UF_Rank[b] {
		UF_Rank[a]++
	}
}
func UF_Find(a int) int {
	if UF_Parent[a] == a {
		return a
	}
	return UF_Find(UF_Parent[a])
}
/*** Union-Find functions ***/

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

/*Union Find*/
int par[100];

void init(int n){
  for(int i = 0; i < n; i++){
    par[i] = i;
  }
}

int find(int x){
  if(par[x] == x) return x;
  return par[x] = find(par[x]);
}

void unite(int x, int y){
  x = find(x);
  y = find(y);
  if(x == y) return;

  par[x] = y;
}

bool same(int x, int y){
  return find(x) == find(y);
}

/*Kruskal*/
struct edge {int u, v, cost;};

bool comp(const edge& e1, const edge& e2){
  return e1.cost < e2.cost;
}

vector<edge> es;
int N, M;

int kruskal(){
  vector<edge>::iterator it = es.begin();
  sort(it, it + M, comp);
  init(N);
  int res = 0;
  for(int i = 0; i < M; i++){
    edge e = es[i];
    if(!same(e.u, e.v)){
      unite(e.u, e.v);
      res += e.cost;
    }
  }
  return res;
}

int main(void){
  while(true){
    int a, b, cost;
    cin >> N >> M;
    if(N == 0 && M == 0) break;
    es.clear();
    for(int i = 0; i < M; i++){
      cin >> a >> b >> cost;
      edge tmp;
      tmp.u = a, tmp.v = b; tmp.cost = cost;
      es.push_back(tmp);
    }
    cout << kruskal() << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <set>
#include <map>
#include <algorithm>
#include <sstream>
//#include <fstream>

using namespace std;

typedef pair<int, int> P;

const int M = 100000;

int prim (vector <vector <int> > t )
{
	int size = t.size();
	vector <int> cost (size, M ); 
	vector <bool> visit (size, false );
	vector <int> path (size, -1 );

	cost[0] = 0;
	int mincost = M;
	int i,p;

	do{
		mincost = M;
		for (i = 0; i < size; ++i){
			if (!visit[i] && mincost > cost[i] ){
				mincost = cost[i];
				p = i;
			} // end if
		} // end for

		visit[p] = true;
		
		for (i = 0; i < size; ++i){
		// m[huÉ×ÚµÄ¢ém[hÅ
		// Ü¾ÜÜêÄ¢È¢m[hÌRXgÌXV
			if (!visit[i] && t[p][i] < cost[i] ){
				cost[i] = t[p][i];
				path[i] = p;
			} // end if
		} // end for

	}while ((int)count (visit.begin(), visit.end(), true ) != size );

	set <P> bridge;

	for (i = size - 1; i > 0; --i){
		int n = i;
		while (n != -1){
			P b(i, path[i] );
			bridge.insert (b );
			n = path[n];
		} // end while
	} // end for

	int res = 0;
	set <P>::iterator it = bridge.begin();
	for (; it != bridge.end(); ++it){
		res += t[(*it).first][(*it).second];		
	} // end for

	return res;
}

int main()
{
//	cut here before submit 
//	freopen ("testcase.stellar", "r", stdin );

	string str = "";
	int n, m;

	while (getline (cin, str ) ){
		stringstream ssn(str);
		ssn >> n >> m;
		
		if (!n && !m ){
			break;
		} // end if

		vector <vector <int> > t (n, vector <int> (n, M ) );
 	
		for (int i = 0; i < m; ++i){
			int from, to, cost;
			getline (cin, str );
			stringstream ss(str);
			ss >> from >> to >> cost;
			t[from][to] = cost;
			t[to][from] = cost;
		} // end for
		
		int res = prim (t );
		cout << res << endl;	

	} // end loop
		
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<queue>
using namespace std;
class Graph {
private:
  const static int INF = 1000000; 
  std::vector<std::vector<int> > edge_;
  unsigned int size_;
public:
  Graph(unsigned int size);
  Graph& connect(int from, int to, int weight);
  std::vector<int> neighbours(int node) const;
  unsigned int size() const;
};

const int Graph::INF;

Graph::Graph(unsigned int size) {
  size_ = size;
  edge_ = std::vector<std::vector<int> > (size_, std::vector<int>(size_, INF));
}

Graph& Graph::connect(int from, int to, int weight = 1) {
  edge_[from][to] = weight;
  return *this;
}

std::vector<int> Graph::neighbours(int node) const {
  std::vector<int> neighbours;
  for (int i = 0; i < static_cast<int>(size_); ++i)
    if (edge_[node][i] < INF) neighbours.push_back(i);

  return neighbours;
}

unsigned int Graph::size() const {
  return size_;
}


Graph creat_graph(int n, int m);
int search_prim(Graph prim, int n);

vector<int> ans;
vector<vector<int>> cost(100,vector<int>(100,0));

int main(){
  int n,m;
 
  
  while(cin >> n >> m, n){     
    Graph prim = creat_graph(n,m);   /*creat graph*/
    ans.push_back(search_prim(prim,n));   /*make answer*/
  }
  
  for(int i: ans){
    cout << i << endl;
  }
  return 0;
}


 Graph creat_graph(int n,int m){
    Graph prim(n);
    int a,b,cost_t;

    for(int i=0; i<m; i++){
      cin >> a >> b >> cost_t;
      prim.connect(a,b);
      cost[a][b] = cost_t;
      cost[b][a] = cost_t;
    }
    return prim;
  }
    
int search_prim(Graph prim, int n){
  int current,cost_sum;
  typedef pair<int, int> PII;
  vector<bool> frag(n,false);
  priority_queue < PII, vector < pair <int, int> >, greater < pair <int, int> > > que;
  /*cost,next_node*/
  
  cost_sum = 0;
  current = 0;
  frag[0] = true;
  for(int k=0; k<n-1; ++k){
     vector<int> near = prim.neighbours(current);

     for(int j:near){
       que.push(PII(cost[current][j],j));
     }

     while(1){
       auto top = que.top();
       que.pop();
       if(frag[top.second] == false){
	 cost_sum += top.first;
	 frag[top.second] = true;
	 current = top.second;
	 break;
	 }
     }  
  }
  return cost_sum;
}