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<cstdio>
#include<algorithm>
#include<vector>
#define rep(i,a) for( int i = 0; i != (a); ++i )

struct edge
{
	int from, to, cost;

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

int n, m;
std::vector<edge> es;

int par[100], rank[100];

void init()
{
	rep( i, n )
		par[i] = i, rank[i] = 0;

	return;
}

int find( int x )
{
	if( x == par[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[y] = x;
	else
	{
		par[x] = y;
		if( rank[x] == rank[y] )
			++rank[y];
	}

	return;
}

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

int main()
{
	while( scanf( "%d%d", &n, &m ), n|m )
	{
		es.clear();
		init();
		rep( i, m )
		{
			int a, b, c;
			scanf( "%d%d%d", &a, &b, &c );
			es.push_back( edge( a, b, c ) );
		}

		std::sort( es.begin(), es.end(), []( const edge& e1, const edge& e2 ){ return e1.cost < e2.cost; } );

		int ans = 0;
		rep( i, es.size() )
		{
			edge& e = es[i];
			if( !same( e.from, e.to ) )
			{
				ans += e.cost;
				unite( e.from, e.to );
			}
		}

		printf( "%d\n", ans );
	}

	return 0;
}

C++: #include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <map>
#include <sstream>
#include <queue>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <iterator>
#include <stack>
#include <list>
using namespace std;
#define INF 1000000000
typedef long long int lli;
typedef pair<int,int> P;

const int MAX_V=100;
int cost[MAX_V][MAX_V];
int mincost[MAX_V];
bool used[MAX_V];

int prim(int V){
	for(int i=0; i<V; ++i){
		mincost[i]=INF;
		used[i]=false;
	}
	mincost[0]=0;
	int res=0;
	
	while(true){
		int v=-1;
		for(int u=0; u<V; ++u){
			if(!used[u]&&(v==-1||mincost[u]<mincost[v])) v=u;
		}
		if(v==-1) break;
		used[v]=true;
		res+=mincost[v];
		for(int u=0; u<V; ++u){
			mincost[u]=min(mincost[u],cost[v][u]);
		}
	}
	return res;
}

int main(){
	int n,m;
	while(cin>>n>>m){
		if(n==0&&m==0) break;
		for(int i=0;i<n;++i)for(int j=0;j<n;++j) cost[i][j]=INF;
		for(int i=0; i<m; ++i){
			int a,b,c;
			cin >> a >> b >> c;
			cost[a][b]=cost[b][a]=c;
		}
		cout << prim(n) << "\n";
	}
	return 0;
}

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

int par[100], rank[100];

void init( int n )
{
	for( int i = 0; i != n; ++i )
	{
		par[i] = i;
		rank[i] = 0;
	}

	return;
}

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];
	}

	return;
}

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

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

int n, m;
std::vector<edge> es;

int main()
{
	while( std::cin >> n >> m, n | m )
	{
		es.clear();

		for( int i = 0; i != m; ++i )
		{
			int a, b, cost;
			std::cin >> a >> b >> cost;
			edge e = { a, b, cost };
			es.push_back( e );
		}

		std::sort( es.begin(), es.end(), []( const edge& e1, const edge& e2 ){ return e1.cost < e2.cost; } );

		init( n );

		int ans = 0;
		for( int i = 0; i != m; ++i )
		{
			if( !same( es[i].from, es[i].to ) )
			{
				ans += es[i].cost;
				unite( es[i].from, es[i].to );
			}
		}

		std::cout << ans << std::endl;
	}

	return 0;
}

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

int par[100], rank[100];

void init( int n )
{
	for( int i = 0; i != n; ++i )
	{
		par[i] = i;
		rank[i] = 0;
	}

	return;
}

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];
	}

	return;
}

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

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

int n, m;
std::vector<edge> es;

int main()
{
	while( std::cin >> n >> m, n | m )
	{
		es.clear();

		for( int i = 0; i != m; ++i )
		{
			int a, b, cost;
			std::cin >> a >> b >> cost;
			edge e = { a, b, cost };
			es.push_back( e );
		}

		std::sort( es.begin(), es.end(), []( const edge& e1, const edge& e2 ){ return e1.cost < e2.cost; } );

		init( n );

		int ans = 0;
		for( int i = 0; i != m; ++i )
		{
			if( !same( es[i].from, es[i].to ) )
			{
				ans += es[i].cost;
				unite( es[i].from, es[i].to );
			}
		}

		std::cout << ans << std::endl;
	}

	return 0;
}