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 <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)

const int INF = 1 << 24;
const int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};

typedef unsigned long long ull;

const int MAX_N = 1000000;

class UnionFind{
public:
    UnionFind(int n){
        REP(i, n){
            par[i] = i;
            rank[i] = 0;
        }
    }
    int find(int x){
        if(x == par[x])return x;
        return par[x] = find(par[x]);
    }
    bool same(int x, int y){
        return find(x) == find(y);
    }
    void unite(int x, int y){
        x = find(x);
        y = find(y);
        if(x == y){return;}

        if(rank[x] > rank[y]){
            par[y] = x;
        }else{
            par[x] = y;
            if(rank[x] == rank[y]){rank[y]++;}
        }
    }
private:
    int rank[MAX_N], par[MAX_N];
};

struct Edge{
    int to, from, cost;
};

bool comp(const Edge& le, const Edge& re){
    return le.cost < re.cost;
}

int N, M;
std::vector<Edge> E;

int kruskal(){
    std::sort(E.begin(), E.end(), comp);

    int res = 0;
    UnionFind uf(N);

    REP(i, M){
        Edge e = E[i];

        if(!uf.same(e.to, e.from)){
            uf.unite(e.to, e.from);
            res += e.cost;
        }
    }

    return res;
}

int main(){
    while(std::cin >> N >> M, N){
        E.clear();
        
        REP(i, M){
            int to, from, cost;
            std::cin >> to >> from >> cost;
            E.push_back({to, from, cost});
        }

        std::cout << kruskal() << std::endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define INF 114514810
#define MOD 1000000007
#define ALL(a) (a).begin(),(a).end()
#define pb(x) push_back(x)
#define ms(m,v) memset(m,v,sizeof(m))
#define D10  fixed<<setprecision(10) 
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int, int> P;
typedef long long ll;
struct edge{ int from, to, cost; };

const int N = 1000;
int par[N]; int hukasa[N];

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

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

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

void init_UFT(int n)
{
	REP(i, n)
	{
		par[i] = i;
		hukasa[i] = 0;
	}
}

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

vector<edge> es;
int main()
{
	int n, m;
	while (cin >> n >> m, n)
	{
		init_UFT(n);
		es.clear();
		int a, b, c;
		REP(i, m)
		{
			cin >> a >> b >> c;
			edge e = { a, b, c };
			es.push_back(e);
		}
		sort(ALL(es), comp);
		int sum = 0;
		REP(i, es.size())
		{
			if (!same(es[i].from, es[i].to))
			{
				unite(es[i].from, es[i].to);
				sum += es[i].cost;
			}
		}
		cout << sum << endl;
	}

	return 0;
}

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

using namespace std;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }

  bool merge(int x, int y){
    int root_x = find(x);
    int root_y = find(y);
    if(root_x != root_y){
      if(data[root_y] < data[root_x]){
	swap(root_x, root_y);
      }
      data[root_x] += data[root_y];
      data[root_y] = root_x;
    }
    
    return root_x != root_y;
  }
  
  int find(int x){
    if(data[x] < 0){
      return x;
    }else{
      return find(data[x]);
    }
  }

  bool is_same(int x, int y){
    return find(x) == find(y);
  }
  
  int size(int x){
    return -find(x);
  }
};

typedef pair<long long int, pair<long long int, long long int> > Edge;

inline Edge make_edge(int a, int b, int c){
  return make_pair(c, make_pair(a, b));
}

int main(int argc, char* argv[]){

  while( true ) {

    long long int n, m;
    cin >> n >> m;
    if ( n == 0 ) break;

    priority_queue< Edge, vector< Edge >, greater< Edge > > q;

    for ( long long int i = 0; i < m; i++ ) {

      long long int a, b, c;
      cin >> a >> b >> c;
      q.push(make_edge(a, b, c));
    }

    
    UnionFind uf(n);
    long long int costs = 0;
    while(!q.empty()){
      Edge edge = q.top(); q.pop();
      const int from = edge.second.first;
      const int to = edge.second.second;

      if(!uf.is_same(from, to)){
	uf.merge(from, to);
	//	cout << edge.first << endl;
	costs += edge.first;
      }
    }
 
    cout << costs << endl;
  }

  return 0;
  
}