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[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){
       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<cmath>
#include<cctype>
#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<deque>
#include<string>
#include<queue>
#include<map>
#include<set>
#include<utility>
#include<queue>

const int MAXN = 105;
using namespace std;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }
  bool unionSet(int x, int y) {
    x = root(x); y = root(y);
    if (x != y) {
      if (data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) {
    return root(x) == root(y);
  }
  int root(int x) {
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x) {
    return -data[root(x)];
  }
};

struct edge{
  edge(int from,int to):from(from),to(to){}
  int from,to;
};

bool operator<(edge a,edge b){
  if(a.from != b.from)return a.from < b.from;
  else return a.to < b.to;
}

typedef pair<int,edge> P;

int main(){
  int n,m;
  while(cin >> n >> m && (n | m) != 0){
    vector<P> road;

    for (int i = 0; i < m; ++i){
      int a,b,c;
      cin >> a >> b >> c;
      road.push_back(make_pair(c,edge(a,b)));
    }
    sort(road.begin(),road.end());
    UnionFind u(MAXN);
    int ans = 0;
    int z = road.size();
    for (int i = 0; i < z; ++i){
      edge top = road[i].second;
      int cost = road[i].first;
      if(!u.findSet(top.to,top.from)){
	//cout << "cost:" << cost << " " << top.to << " " << top.from << endl;
	ans += cost;
	u.unionSet(top.to, top.from);
      }
    }
    cout << ans << endl;
  }
  return 0;
}

C++: #include<iostream>
using namespace std;
#include<vector>
struct UF{
	int n;
	vector<int>parent,rank;
	UF(int n_=0):n(n_),parent(n_),rank(n_,0)
	{
		for(int i=0;i<n_;i++)parent[i]=i;
	}
	int find(int a)
	{
		return parent[a]!=a?parent[a]=find(parent[a]):a;
	}
	bool same(int a,int b)
	{
		return find(a)==find(b);
	}
	bool unite(int a,int b)
	{
		a=find(a),b=find(b);
		if(a==b)return false;
		if(rank[a]<rank[b])
		{
			parent[a]=b;
		}
		else
		{
			parent[b]=a;
			if(rank[a]==rank[b])rank[a]++;
		}
		return true;
	}
};
#include<algorithm>
#include<vector>
int n,m;
main()
{
	while(cin>>n>>m,n)
	{
		vector<pair<int,pair<int,int> > >e;
		for(int i=0;i<m;i++)
		{
			int a,b,c;cin>>a>>b>>c;
			e.push_back(make_pair(c,make_pair(a,b)));
		}
		UF uf(n);
		sort(e.begin(),e.end());
		int ans=0;
		for(int i=0;i<m;i++)
		{
			int a=e[i].second.first,b=e[i].second.second,c=e[i].first;
			if(uf.same(a,b))continue;
			uf.unite(a,b);
			ans+=c;
		}
		cout<<ans<<endl;
	}
}