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----------------------------------------------------------------------------------------------------------------------
#include <bits/stdc++.h>

//using namespace--------------------------------------------------------------------------------------------------------------
using namespace std;

//define-----------------------------------------------------------------------------------------------------------------------
#define rep(i, n) for(int i = 0; i < n; i++)
#define FOR(i, s, n) for(int i = s; i < n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << endl
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define FOREACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define INF 1 << 25
#define CLR(a) memset((a), 0 ,sizeof(a))
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define sq(n) (n) * (n)

//typedef----------------------------------------------------------------------------------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef unsigned int uint;
typedef unsigned long long ull;

//const------------------------------------------------------------------------------------------------------------------------
const double EPS = 1e-10;
const double PI = acos( -1.0 );

//global-----------------------------------------------------------------------------------------------------------------------
int n, m;
int cost[ 100 ][ 100 ];
bool visit[ 100 ];
int a, b, c;

//function---------------------------------------------------------------------------------------------------------------------

int main() {
	while ( scanf( "%d %d", &n, &m ) != 0 ) {
		if ( n == 0 && m == 0 )
			return 0;
		rep( i, n ) {
			rep( j, n ) {
				cost[ i ][ j ] = INF;
				if ( i == j )
					cost[ i ][ j ] = 0;
			}
			visit[ i ] = false;
		}
		rep( i, m ) {
			scanf( "%d %d %d", &a, &b, &c );
			cost[ a ][ b ] = c;
			cost[ b ][ a ] = c;
		}
		int ans = 0;
		visit[ 0 ] = true;
		FOR( i, 1, n ) {
			int min_cost = INF;
			int can_visit;
			rep( j, n ) {
				if ( !visit[ j ] )
					continue;
				rep( k, n ) {
					if ( cost[ j ][ k ] < min_cost && !visit[ k ] ) {
						min_cost = cost[ j ][ k ];
						can_visit = k;
					}
				}
			}
			ans += min_cost;
			visit[ can_visit ] = true;
		}
		printf( "%d\n", ans );
	}
	return 0;
}

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

struct edge{ int to, cost; };
typedef pair<int, int> P;

int m, n;

int main()
{
    while(cin >> n >> m && n) {
        int a,b,cost;
        vector<vector<edge> > es(n);
        for(int i = 0; i < m; i++) {
            cin >> a >> b >> cost;
            es[a].push_back((edge){b, cost});
            es[b].push_back((edge){a, cost});
        }

        int ans = 0;
        priority_queue< P, vector<P>, greater<P> > que;
        que.push(P(0, 0));
        bool visit[n];
        fill(visit, visit + n, false);
        while(!que.empty()) {
            P p = que.top(); que.pop();
            if(visit[p.second]) 
                continue;
            
            visit[p.second] = true;
            ans += p.first;
            
            for(int i = 0; i < es[p.second].size(); i++)
                que.push(P(es[p.second][i].cost, es[p.second][i].to));
        }
        cout << ans << endl;
    }
}