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 <queue>
#include <vector>

using namespace std;

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

	Bridge() : from(0), to(0), cost(0) {}
	Bridge(const Bridge& b) : from(b.from), to(b.to), cost(b.cost) {}

	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++)
		{
			bridge[i] = Bridge();
			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();

			if(city[current.to] && city[current.from])
			{
				continue;
			}

			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 || bridge[i].from == next)
				{
					if(!city[bridge[i].to] || !city[bridge[i].from])
					{
						que.push(bridge[i]);
					}
				}
			}
		}

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

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 1000000007
#define EPS 1e-10

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;
typedef pair<P, char> PC;

set<int> si;

int n, m;
int a, b, cost;
int d[110];
bool used[110];

struct edge{
	int to, cost;
	edge(int _to, int _cost) :to(_to), cost(_cost){};
};

vector<edge> G[110];

void prim(int s){
	fill(d, d + 110, INF);
	REP(i, n)used[i] = false;
	d[s] = 0;
	priority_queue<P,vector<P>,greater<P>> que;
	que.push(P(0, s));

	while (!que.empty()){
		P p = que.top(); que.pop();
		int v = p.second;

		if (used[v])continue;

		used[v] = 1;

		for (int i = 0; i < G[v].size(); i++){
			edge e = G[v][i];
			if (used[e.to])continue;
			if (d[e.to] > e.cost){
				d[e.to] = e.cost;
				que.push(P(d[e.to], e.to));
			}
		}
	}
}

int main(){
	while (cin >> n >> m&&n + m){
		REP(i, m){
			cin >> a >> b >> cost;
			G[a].push_back(edge(b, cost));
			G[b].push_back(edge(a, cost));
		}
		prim(0);
		int ans = 0;
		REP(i, n){
			ans += d[i];
		}
		cout << ans << endl;
		REP(i, n)G[i].clear();
	}
}

C++: #include <iostream>
#define TOSHI_MAX 100
#define COST_MAX 100000
using namespace std;

int prim(int data[TOSHI_MAX][TOSHI_MAX], int toshiNum) {
  bool visited[toshiNum];
  int cost[toshiNum];
  for(int i = 0; i < toshiNum; i++) {
    visited[i] = false;
    cost[i] = COST_MAX;
  }
  cost[0] = 0;
  while(1) {
    int min = COST_MAX;
    int p;
    for(int i = 0; i < toshiNum; i++) {
      if(!visited[i] && cost[i] < min) {
	min = cost[i];
	p = i;
      }
    }
    if(min == COST_MAX) break;

    visited[p] = true;
    for(int i = 0; i < toshiNum; i++) {
      if(!visited[i] && data[p][i] < cost[i]) {
	cost[i] = data[p][i];
      }
    }
  }

  int ans = 0;
  for(int i = 0; i < toshiNum; i++) {
    if(cost[i] != COST_MAX) ans += cost[i];
  }

  return ans;
}

int main() {
  while(1) {
    int n, m;
    cin >> n >> m;
    if(n == 0 && m == 0) break;

    int data[TOSHI_MAX][TOSHI_MAX];
    for(int i = 0; i < n; i++) {
      for(int j = 0; j < n; j++) {
	data[i][j] = COST_MAX;
      }
    }

    for(int i = 0; i < m; i++) {
      int a, b, cost;
      cin >> a >> b >> cost;
      data[a][b] = data[b][a] = cost;
    }

    cout << prim(data, n) << endl;
  }

  return 0;
}