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<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[a][b] = 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){
       if(frag[que.top().second] == false){
	 cost_sum += que.top().first;
	 frag[que.top().second] = true;
	 current = que.top().second;
	 break;
	 }
     }
     que.pop();
  }
  return cost_sum;
}

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

template<typename T>
struct Kruskal{
    struct edge{
        int from,to,used; T cost;
        edge(int from,int to,T cost):
            from(from),to(to),cost(cost),used(0){}
        bool operator<(const edge &e) const{
            if (cost!=e.cost) return cost<e.cost;
            else if (from!=e.from) return from<e.from;
            else return to<e.to;
        }
    };
    int num;
    vector<int> par,rank;
    vector<edge> es;
    Kruskal(int n):num(n),par(n),rank(n,1){
        iota(par.begin(),par.end(),0);
    }
    int root(int x){
        if (par[x]==x) return x;
        return par[x]=root(par[x]);
    }
    bool merge(int x, int y){
        x=root(x),y=root(y);
        if (x==y) return false;
        if (rank[x]<rank[y]) swap(x,y);
        par[y]=x;
        rank[x]+=rank[y];
        --num;
        return true;
    }
    bool same(int x, int y){return root(x)==root(y);}
    int size(int x){return rank[root(x)];}
    int count(){return num;}
    void add_edge(int u,int v,T c){
        es.emplace_back(u,v,c);
    }
    T build(){
        sort(es.begin(),es.end());
        T res=0;
        for (auto &e:es){
            if (!same(e.from,e.to)){
                res+=e.cost;
                merge(e.from,e.to);
                e.used=1;
            }
        }
        return res;
    }
    vector<int> used_es(T &c){
        int E=es.size();
        map<edge,int> m;
        for (int i=0;i<E;++i) m[es[i]]=i;
        c=build();
        vector<int> list(E);
        for (int i=0;i<E;++i) list[m[es[i]]]=es[i].used;
        return list;
    }
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n,m;
    while(cin >> n >> m,n,m){
        Kruskal<int> K(n);
        for (int i=0;i<m;++i){
            int a,b,cost; cin >> a >> b >> cost;
            K.add_edge(a,b,cost);
        }
        cout << K.build() << '\n';
    }
}