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 <bits/stdc++.h>
using namespace std;
#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define INF 114514810
#define MOD 1000000007
#define ALL(a) (a).begin(),(a).end()
#define pb(x) push_back(x)
#define ms(m,v) memset(m,v,sizeof(m))
#define D10  fixed<<setprecision(10) 
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int, int> P;
typedef long long ll;
struct edge{ int from, to, cost; };

int par[10000]; int hukasa[10000];

int find(int x)
{
	if (par[x] == x) return x;
	else par[x] = find(par[x]);
}

void unite(int x, int y)
{
	x = find(x); y = find(y);
	if (x == y) return;
	if (hukasa[x] < hukasa[y]) par[x] = y;
	else
	{
		par[y] = x;
		if (hukasa[x] == hukasa[y]) hukasa[x]++;
	}
}

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

void init_UFT(int n)
{
	REP(i, n)
	{
		par[i] = i;
		hukasa[i] = 0;
	}
}

bool comp(const edge& e1, const edge& e2)
{
	return e1.cost < e2.cost;
}

vector<edge> es;
int main()
{
	int n, m;
	while (cin >> n >> m, n)
	{
		init_UFT(n);
		es.clear();
		int a, b, c;
		REP(i, m)
		{
			cin >> a >> b >> c;
			edge e = { a, b, c };
			es.push_back(e);
		}
		sort(ALL(es), comp);
		int sum = 0;
		REP(i, es.size())
		{
			if (!same(es[i].from, es[i].to))
			{
				unite(es[i].from, es[i].to);
				sum += es[i].cost;
			}
		}
		cout << sum << endl;
	}

	return 0;
}

C++: #include <iostream>

using namespace std;
static const int INF = 99999999;
int cost[101][101];
int mincost[101];
bool used[101];
int n, m;

int prim()
{
	for(int u = 0; u < 101; ++u)
	{
		mincost[u] = INF;
		used[u] = false;
	}
	mincost[0] = 0;
	int res = 0;
	while(true)
	{
		int v = -1;
		for(int u = 0; u < n; ++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 < n; ++u)
		{
			mincost[u] = min(mincost[u], cost[v][u]);
		}
	}
	return(res);
}

void solve()
{
	while(cin >> n >> m, n || m)
	{
		for(int i = 0; i < 101; ++i)
		{
			for(int j = 0; j < 101; ++j)
			{
				cost[i][j] = INF;
			}
		}
		for(int i = 0; i < m; ++i)
		{
			int a, b, c;
			cin >> a >> b >> c;
			cost[a][b] = c;
			cost[b][a] = c;
		}
		cout << prim() << endl;
	}
}

int main()
{
	solve();
	return(0);
}

C++: #include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

int cost[110][110];
bool used[110];

int main() {
	int n,m;
	int a,b,c;
	while(n=in(),m=in()){
		int i,j;
		for(i=0;i<110;i++){
			for(j=0;j<100;j++){
				cost[i][j]=1000;
			}
			used[i]=false;
		}
		for(i=0;i<m;i++){
			cin>>a>>b>>c;
			if(cost[a][b]>c){
				cost[a][b]=c;
				cost[b][a]=c;
			}
		}
		priority_queue<pint,vector<pint>,greater<pint> > que;
		que.push(pint(0,0));
		int res=0;
		while(!que.empty()){
			pint p=que.top();
			que.pop();
			if(used[p.second])continue;
			used[p.second]=true;
			res+=p.first;
//cout<<p.first<<" "<<p.second<<endl;
			for(i=0;i<n;i++){
				if(used[i])continue;
				if(cost[p.second][i]==1000)continue;
				que.push(pint(cost[p.second][i],i));
			}
		}
		cout<<res<<endl;
	}
	return 0;
}