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 <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

template <typename T>
struct edge {
    int from, to;
    T cost;

    edge(int to, T cost) : from(-1), to(to), cost(cost) {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost) {}

    explicit operator int() const {return to;}
};

class UnionFind {
    vector<int> uni;
    int n;
public:
    explicit UnionFind(int n) : uni(static_cast<u32>(n), -1) , n(n){};

    int root(int a){
        if (uni[a] < 0) return a;
        else return (uni[a] = root(uni[a]));
    }

    bool unite(int a, int b) {
        a = root(a);
        b = root(b);
        if(a == b) return false;
        if(uni[a] > uni[b]) swap(a, b);
        uni[a] += uni[b];
        uni[b] = a;
        return true;
    }
};

template< typename T >
T kruskal(vector<edge<T>> &G, int V)
{
    sort(begin(G), end(G), [](const edge< T > &a, const edge< T > &b) { return (a.cost < b.cost); });
    UnionFind tree(V);
    T ret = 0;
    for(auto &e : G) {
        if(tree.unite(e.from, e.to)) ret += e.cost;
    }
    return (ret);
}

int main() {
    int n, m;
    while(cin >> n >> m, n){
        vector<edge<int>> G;
        for (int i = 0; i < m; ++i) {
            int a, b, c;
            scanf("%d %d %d", &a, &b, &c);
            G.emplace_back(a, b, c);
        }
        cout << kruskal(G, n) << "\n";
    }
    return 0;
}

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

#define rep(i,n) for(int i=0;i<(int)n;++i)
#define foreach(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;


pair<Weight, Edges> minimumSpanningTree(const Graph &g, int r = 0) {
  int n = g.size();
  Edges T;
  Weight total = 0;

  vector<bool> visited(n);
  priority_queue<Edge> Q;
  Q.push( Edge(-1, r, 0) );
  while (!Q.empty()) {
    Edge e = Q.top(); Q.pop();
    if (visited[e.dst]) continue;
    T.push_back(e);
    total += e.weight;
    visited[e.dst] = true;
    foreach(f, g[e.dst]) if (!visited[f->dst]) Q.push(*f);
  }
  return pair<Weight, Edges>(total, T);
}

int main() {
	int n,m;
	while(cin>>n>>m,n){
		Graph g(n);
		rep(i,m){
			int a,b,c; cin>>a>>b>>c;
			g[a].push_back(Edge(a,b,c));
			g[b].push_back(Edge(b,a,c));
		}
		cout<<minimumSpanningTree(g).first<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <utility>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <cmath>
#include <cassert>
#include <queue>
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
const int INF = 1<<30;
const int MOD = 1e9 + 7;
struct edge
{
    int to, cost;
    edge(int to, int cost) { this->to = to, this->cost = cost; }
};
int n, m;
int MST(vector<edge> G[])
{
    priority_queue<P, vector<P>, greater<P>> que;
    vector<int> used(n, 0);
    que.push(make_pair(0, 0));
    int res = 0;
    while(que.size())
    {
        P p = que.top(); que.pop();
        int v = p.second;
        if(used[v]) continue;
        used[v] = 1;
        res += p.first;
        for(int u = 0; u < G[v].size(); u++)
        {
            edge e = G[v][u];
            que.push(make_pair(e.cost, e.to));
        }
    }
    return res;
}
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    while(cin >> n >> m, n | m)
    {
        vector<edge> G[n];
        for(int i = 0; i < m; i++)
        {
            int a, b, c; cin >> a >> b >> c;
            G[a].push_back(edge(b, c));
            G[b].push_back(edge(a, c));
        }
        cout << MST(G) << endl;
    }
    return 0;
}