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++: // http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0180
// PCK2008yosen-08
// パソコン甲子園・・・チームrand()・・・うっ・・・高校時代も今もあいつらとは目を合わせないように生きてきたんだ・・・

#include <cstdio>
#include <algorithm>
using namespace std;

struct bridge {
	int a;
	int b;
	int cost;
	
	bool operator < ( const bridge& com ) const {
		return (this->cost < com.cost);
	};
};

int root[110];
bridge br[10010];

int getroot(int city) {
	if ( root[city] == city ) {
		return city;
	}
	root[city] = getroot(root[city]);
	return root[city];
}

int main(void) {
	
	while(true) {
		int n, m;
		scanf("%d %d", &n, &m);
		if ( n == 0 ) { return 0; }
		for(int i=0; i<m; i++) {
			scanf("%d %d %d", &br[i].a, &br[i].b, &br[i].cost);
		}
		
		sort(br, br+m);
		
		for(int i=0; i<n; i++) {
			root[i] = i;
		}
		
		int total = 0;
		for(int i=0; i<m; i++) {
			if ( getroot(br[i].a) == getroot(br[i].b) ) { continue; }
			
			// 橋を追加
			total += br[i].cost;
			int ra = getroot(br[i].a);
			int rb = getroot(br[i].b);
			root[ra] = rb;
			
			int j;
			for(j=1; j<n; j++) {
				if (getroot(j) != getroot(0)) {
					break;
				}
			}
			/*
			for(int aa=0; aa<n; aa++) {
				printf("%d ", root[aa]);
			}
			printf("\n");
			*/
			if ( j == n ) { break; }
		}
		
		printf("%d\n", total);
	}

}

C++: #include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<cctype>
#include<complex>
#include<iostream>
#include<sstream>
#include<algorithm>
#include<functional>
#include<vector>
#include<string>
#include<stack>
#include<queue>
#include<map>

using namespace std;
const int dx[] = {1,0,-1,0},dy[] = {0,1,0,-1};
#define INF 1e+8
#define rep(i,j) for(int i = 0; i < (j); i++)
#define reps(i,j,k) for(int i = j; i < k; i++)
typedef long long ll;
typedef unsigned long long ull;
int par[128];
int rank[128];
struct edge{
	int from,to,cst;
};
bool cmp(const edge& left, const edge& right){
	return left.cst < right.cst;
}
void init(int n){
	rep(i,n){
		par[i] = i;
		rank[i] = 0;
	}
}
int find(int x){
	if(par[x] == x)return x;
	else return par[x] = find(par[x]);
}
void unite(int x,int y){
	x = find(x);
	y = find(y);
	if(x == y)return ;
	if(rank[x] < rank[y]){
		par[x] = y;
	}
	else{
		par[y] = x;
		if(rank[x] == rank[y])rank[x]++;
	}
}
bool same(int x,int y){
	return find(x) == find(y);
}
int main(){
	int n,m;
	while(scanf("%d%d",&n,&m),n|m){
		edge Data[128];
		rep(i,m){
			scanf("%d%d%d",&Data[i].from,&Data[i].to,&Data[i].cst);
		}
		sort(Data,Data+m,cmp);
		init(n);
		int ans = 0;
		rep(i,m){
			edge next = Data[i];
			if(!same(next.from, next.to)){
				unite(next.from,next.to);
				ans += next.cst;
			}
		}
		printf("%d\n",ans);
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#define rep(i,n) for(int i=0;i<n;i++)
//#define int long long
using namespace std;

#define INF 999999

int n, m;
int a, b, c;

int cost[100][100];
int mincost[100];
bool used[100];

void init()
{
	rep(i,100) rep(j,100)
	{
		cost[i][j] = INF;
	}
}

int prim()
{
	rep(i,n)
	{
		mincost[i] = INF;
		used[i] = false;
	}

	mincost[0] = 0;
	int res = 0;

	while (true)
	{
		int v = -1;
		rep(u,n)
		{
			if (!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
		}

		if (v == -1) break;
		used[v] = true;
		res += mincost[v];

		rep(u,n)
		{
			mincost[u] = min(mincost[u], cost[v][u]);
		}
	}

	return res;
}

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

		init();

		rep(i,m)
		{
			cin >> a >> b >> c;
			cost[a][b] = c;
			cost[b][a] = c;
		}

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

C++: #include <bits/stdc++.h>

using namespace std;

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

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pll> pip;
const ll INF = 1ll<<60;
const ll MOD = 1000000007;
const double EPS  = 1e-9;

struct UnionFind {
	vector<int> par;
	vector<int> rank;
	
	UnionFind() {}
	UnionFind(int n) {
		init(n);
	}
	
	int operator[] (int x) {
		return find(x);
	}

	void init(int n) {
		par.resize(n);
		rank.resize(n);
		REP(i, n) {
			par[i] = i;
			rank[i] = 0;
		}
	}

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

	void unite(int x, int y) {
		x = find(x);
		y = find(y);
		if (x == y) return;

		if (rank[x] < rank[y]) {
			par[x] = y;
		} else {
			par[y] = x;
			if (rank[x] == rank[y]) rank[x]++;
		}
	}

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

int main() {
	int n, m;
	while (cin >> n >> m, n || m) {
		
		priority_queue<pip, vector<pip>, greater<pip> > pq;
		REP(i, m) {
			int a, b, c;
			scanf("%d %d %d", &a, &b, &c);
			pq.push(pip(c, pii(a, b)));
		}
		
		UnionFind uf(n);
		int ans = 0;
		while (!pq.empty()) {
			pip now = pq.top(); pq.pop();
			
			int c = now.fi;
			int u = now.se.fi, v = now.se.se;
			
			if (uf.same(u, v)) continue;
			ans += c;
			uf.unite(u, v);
		}
		cout << ans << endl;
	}
	return 0;
}