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 <iomanip>
#include <sstream>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
#include <functional>
#include <iterator>
#include <limits>
#include <numeric>
#include <utility>
#include <cmath>
#include <cassert>

using namespace std; using namespace placeholders;

typedef long long LL;
typedef unsigned long long ULL;
typedef vector< int > VI;
typedef vector< VI > VVI;
typedef vector< string > VS;
typedef stringstream SS;
typedef pair< int, int > PII;
typedef vector< pair< int, int > > VPII;
#define VT( type ) vector< type >
#define VVT( type ) vector< vector< type > >
#define LIM( type ) numeric_limits< type >

template < typename T > inline istream& operator>>( istream &s, vector< T > &v ){ for ( T &t : v ) { s >> t; } return s; }
template < typename T > inline void input_n( vector< T > &out ) { copy_n( istream_iterator< T >( cin ), out.size(), out.begin() ); };
template < typename T > inline T fromString( const string &s ) { T res; istringstream iss( s ); iss >> res; return res; };
template < typename T > inline string toString( const T &a ) { ostringstream oss; oss << a; return oss.str(); };

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); ++i )
#define FOR( e, c ) for ( auto &e : c )
#define ALL( c ) (c).begin(), (c).end()
#define AALL( a, t ) (t*)a, (t*)a + sizeof( a ) / sizeof( t )
#define DRANGE( c, p ) (c).begin(), (c).begin() + p, (c).end()

#define SZ( v ) ( (int)( v ).size() )
#define PB push_back
#define EM emplace
#define EB emplace_back
#define BI back_inserter

#define EXIST( c, e ) ( ( c ).find( e ) != ( c ).end() )

#define MP make_pair
#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

// Prim 法による MST
#include <vector>
#include <utility>
#include <queue>
#include <limits>
#include <type_traits>
namespace MinimumSpanningTree
{
	template < typename COST_TYPE = int, typename = typename std::enable_if< std::is_arithmetic< COST_TYPE >::value >::type >
	class Prim
	{
		using Edge = std::pair< COST_TYPE, int >;
		const COST_TYPE INF = std::numeric_limits< COST_TYPE >::max() / 2;

		const int N;
		std::vector< std::vector< Edge > > G;

	public:
		Prim( const int n ) : N( n ), G( N )
		{
			return;
		}

		void connect( const int u, const int v, COST_TYPE c )
		{
			G[u].emplace_back( c, v );
			G[v].emplace_back( c, u );

			return;
		}

		COST_TYPE solve()
		{
			std::vector< COST_TYPE > costs( N, INF );
			costs[0] = 0;

			std::vector< bool > used( N );

			std::priority_queue< Edge, std::vector< Edge >, greater< Edge > > que;
			que.emplace( 0, 0 );

			COST_TYPE result = 0;

			while ( !que.empty() )
			{
				const COST_TYPE cost = que.top().first;
				const int u = que.top().second;
				que.pop();

				if ( used[u] )
				{
					continue;
				}

				used[u] = true;
				result += cost;

				for ( Edge &e : G[u] )
				{
					const COST_TYPE c = e.first;
					const int v = e.second;

					if ( c < costs[v] )
					{
						que.emplace( costs[v] = c, v );
					}
				}
			}

			return result;
		}
	};
}
// MinimumSpanningTree::Prim( |V| )
// connect( u, v, cost )
// solve()

int solve( const int N, const int M )
{
	MinimumSpanningTree::Prim<> prim( N );
	REP( i, 0, M )
	{
		int a, b, c;
		cin >> a >> b >> c;
		prim.connect( a, b, c );
	}

	return prim.solve();
}

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	for ( int n, m; cin >> n >> m, ( n | m ); cout << solve( n, m ) << endl );

	return 0;
}

C++: #include<stdio.h>
#include<string.h>
#include<math.h>
int main(void)
{
	int a,s,d[101],f[101],g[101],h,i,j,size[101],ban[101];
	int z,x,q;
	while(1){
		q=0;
		scanf("%d %d",&a,&s);
		if(a==0&&s==0) break;
		for(i=0;i<a;i++){
			ban[i]=i;
			size[i]=1;
		}
		for(i=0;i<s;i++) scanf("%d %d %d",&d[i],&f[i],&g[i]);
		for(i=0;i<s;i++){
			if(d[i]>f[i]) h=d[i]; d[i]=f[i]; f[i]=h;
			for(j=i+1;j<s;j++){
				if(g[i]>g[j]){
					h=g[i]; g[i]=g[j]; g[j]=h;
					h=d[i]; d[i]=d[j]; d[j]=h;
					h=f[i]; f[i]=f[j]; f[j]=h;
				}
			}
		}
		for(i=0;i<s;i++){
			z=d[i]; x=f[i];
			while(ban[z]!=z) z=ban[z];
			while(ban[x]!=x) x=ban[x];
			if(z!=x){
				q+=g[i];
				if(size[z]>size[x]) ban[z]=x;
				else if(size[z]<size[x]) ban[x]=z;
				else{
					ban[x]=z;
					size[x]++;
				}
			}
		}
		printf("%d\n",q);
	}
	return 0;
}