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 <sstream>
#include <fstream>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <numeric>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
using namespace std;

#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()

typedef int Weight;
struct Edge {
  int src, dst;
  Weight weight;
  Edge(int src, int dst, Weight weight) :
    src(src), dst(dst), weight(weight) { }
};
bool operator < (const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
    e.src != f.src ? e.src < f.src : e.dst < f.dst;
}
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

typedef vector<Weight> Array;
typedef vector<Array> Matrix;

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)];
  }
};

pair<Weight, Edges> minimumSpanningForest(const Graph &g) {
  int n = g.size();
  UnionFind uf(n);
  priority_queue<Edge> Q;
  REP(u, n) FOR(e, g[u]) if (u < e->dst) Q.push(*e);

  Weight total = 0;
  Edges F;
  while ((int)F.size() < n-1 && !Q.empty()) {
    Edge e = Q.top(); Q.pop();
    if (uf.unionSet(e.src, e.dst)) {
      F.push_back(e);
      total += e.weight;
    }
  }
  return pair<Weight, Edges>(total, F);
}

int main() {
    int n, m;
    while ( cin >> n >> m ) {
        if ( n == 0 && m == 0 ) break;
        Graph g(n);
        int sum = 0;
        for ( int i = 0; i < m; i++ ) {
            int a, b, c;
            cin >> a >> b >> c;
            g[a].push_back( Edge( a, b, c ) );
            g[b].push_back( Edge( b, a, c ) );
            sum += c;
        }

        cout << minimumSpanningForest(g).first << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <functional>

using namespace std;
static const int INF = 999999;
int V, E;
struct SEdge
{
	int From;
	int To;
	int Cost;
};
vector<SEdge> Edge;

vector<int> par;
vector<int> rank;

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

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

void unite(int x, int y)
{
	x = find(x);
	y = find(y);
	if(x == y)
	{
		return;
	}
	if(rank[x] < rank[y])
	{
		par[x] = y;
	}
	else
	{
		par[y] = x;
		if(rank[x] == rank[y])
		{
			++rank[x];
		}
	}
}

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

bool comp(const SEdge& e1, const SEdge& e2)
{
	return(e1.Cost < e2.Cost);
}

int Kruskal()
{
	init(V);
	sort(Edge.begin(), Edge.end(), comp);
	int res = 0;
	for(int i = 0; i < E; ++i)
	{
		SEdge e = Edge[i];
		if(!same(e.From, e.To))
		{
			unite(e.From, e.To);
			res += e.Cost;
		}
	}
	return(res);
}

void solve()
{
	while(cin >> V >> E, V || E)
	{
		Edge.clear();
		Edge.resize(E);
		for(int i = 0; i < E; ++i)
		{
			SEdge e;
			cin >> e.From >> e.To >> e.Cost;
			Edge[i] = e;
		}
		cout << Kruskal() << endl;
	}
}

int main()
{
	solve();
	return(0);
}