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

#define rep(i, n) for(int i = 0; i < n; i ++)
#define COUNT(i, n) for(int i = 1; i <= n; i ++)
#define ALL(T) T.begin(), T.end()
#define mp make_pair
#define pb push_back
#define ITER(c) __typeof((c).begin())
#define each(c, it) for(ITER(c) it = (c).begin(); it != (c).end(); it++)
#define C first
#define S second.first
#define Z second.second

using namespace std;

typedef pair<int, int> pii;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<string> vs;

const int INF = 1 << 24;
const int N = 100;

int n;
bool ok[N][N];
int c[N][N];

bool check();

int main(void){
    for(int m, res; cin >> n >> m, n; cout << res << endl){
        res = 0;
        rep(i, n) rep(j, n) ok[i][j] = false, c[i][j] = 0;

        vector< pair<int, pii> > in;
        while(m--){
            int a, b, cost; cin >> a >> b >> cost;

            ok[a][b] = ok[b][a] = true;
            c[a][b] = c[b][a] = cost;
            in.pb(mp(cost, mp(a, b)));
        }
        sort(ALL(in), greater< pair<int, pii> >());

        rep(i, in.size()){
            int a = in[i].S, b = in[i].Z;
            ok[a][b] = false;
            ok[b][a] = false;

            if(!check()){
                ok[a][b] = true;
                ok[b][a] = true;
            }
        }

        rep(i, n) for(int j = i + 1; j < n; j++) if(ok[i][j]) res += c[i][j];
    }

    return 0;
}

bool check(){
    vector<bool> used(n);
    
    queue<int> q;
    q.push(0);

    while(!q.empty()){
        int cur = q.front(); q.pop();
        if(used[cur]) continue;
        used[cur] = true;

        rep(next, n) if(ok[cur][next]) q.push(next);
    }

    return !count(ALL(used), false);
}

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

struct Dset {
  Dset *parent;
  int rank;

  Dset() {
    clear();
  }

  void clear() {
    parent = NULL;
    rank = 0;
  }

  Dset *find() {
    if (!parent) {
      return this;
    } else {
      parent = parent->find();
      return parent;
    }
  }

  bool merge(Dset *a) {
    Dset *myRoot = find();
    Dset *yourRoot = a->find();
    if (myRoot->rank < yourRoot->rank) {
      myRoot->parent = yourRoot;
    } else if (myRoot->rank > yourRoot->rank) {
      yourRoot->parent = myRoot;
    } else if (myRoot != yourRoot) {
      yourRoot->parent = myRoot;
      myRoot->rank++;
    } else {
      return false;
    }
    return true;
  }
};

struct Bridge {
  int a;
  int b;
  int cost;
  
  bool operator<(const Bridge &obj) const {
    return (cost < obj.cost);
  }
};

int main() {
  int n, m, ans;
  Bridge bridge[6000];
  Dset x[100];
  while (1) {
    cin >> n >> m;
    if (!n && !m) break;
    for (int i=0; i<m; i++) {
      cin >> bridge[i].a >> bridge[i].b >> bridge[i].cost;
    }
    sort(bridge, bridge+m);
    for (int i=0; i<n; i++) {
      x[i].clear();
    }
    ans = 0;
    for (int i=0; i<m; i++) {
      if (x[bridge[i].a].merge(&x[bridge[i].b])) {
        ans += bridge[i].cost;
      }
    }
    cout << ans << endl;
  }

  return 0;
}

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

using namespace std;

class Bridge
{
public:
	int from;
	int to;
	int cost;

	Bridge() : from(0), to(0), cost(0) {}

	bool operator > (const Bridge& b) const
	{
		return cost > b.cost;
	}

	bool operator < (const Bridge& b) const
	{
		return cost < b.cost;
	}
};



int nCity, nBridge;

Bridge bridge[100];
bool city[100];

int main()
{
	while( 1 )
	{
		//load data
		cin >> nCity >> nBridge;
		if(nCity == 0 && nBridge == 0)
		{
			break;
		}

		for(int i=0; i<nBridge; i++)
		{
			cin >> bridge[i].from >> bridge[i].to >> bridge[i].cost;
		}

		for(int i=0; i<nCity; i++)
		{
			city[i] = false;
		}

		//set initial node to queue
		priority_queue<Bridge, vector<Bridge>, greater<Bridge> > que;
		for(int i=0; i<nBridge; i++)
		{
			if(bridge[i].from == 0 || bridge[i].to == 0)
			{
				que.push(bridge[i]);
			}
		}

		city[0] = true;

		//iteration
		int totalCost = 0;
		while(!que.empty())
		{
			//end check
			bool isEnd = true;
			for(int i=0; i<nCity; i++)
			{
				if(!city[i])
				{
					isEnd = false;
					break;
				}
			}

			if(isEnd)
			{
				break;
			}

			//check highest priority node
			Bridge current = que.top();
			que.pop();

			totalCost += current.cost;

			int next = 0;
			if(!city[current.to])
			{
				city[current.to] = true;
				next = current.to;
			}
		
			if(!city[current.from])
			{
				city[current.from] = true;
				next = current.from;
			}

			for(int i=0; i<nBridge; i++)
			{
				if((bridge[i].to == next && !city[bridge[i].from]) || 
				   (bridge[i].from == next && !city[bridge[i].to]))
				{
					que.push(bridge[i]);
				}
			}

			break;
		}

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