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 pb(n) push_back(n)
#define fi first
#define se second
#define all(r) (r).begin(),(r).end()
#define gsort(st,en) sort((st),(en),greater<int>())
#define vmax(ary) *max_element(all(ary))
#define vmin(ary) *min_element(all(ary))
#define debug(x) cout<<#x<<": "<<x<<endl
#define fcout(n) cout<<fixed<<setprecision((n))
#define scout(n) cout<<setw(n)
#define vary(type,name,size,init) vector< type> name(size,init)

#define rep(i,n) for(int i = 0; i < (int)(n);++i)
#define REP(i,a,b) for(int i = (a);i < (int)(b);++i)
#define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it)
#define repa(n,array) for(auto &n :(array))

using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using dict = map<string,int>;
using pii = pair<int,int> ;

const int mod = 1000000007;
constexpr int imax = ((1<<30)-1)*2+1 ;
constexpr int inf = 100000000;
constexpr double PI = acos(-1.0) ;
double eps = 1e-10 ;
const int dy[] = {-1,0,1,0};
const int dx[] = {0,-1,0,1};

inline bool value(int x,int y,int w,int h){
  return (x >= 0 && x < w && y >= 0 && y < h);
}

template<typename T>
void Unique(vector<T> &v){
  sort(all(v));
  v.erase(unique(all(v)),v.end());
}

template<typename T>
T ston(string& str, T n){
  istringstream sin(str) ;
  T num ;
  sin >> num ;
  return num ;
}

void Ans(bool f){
  if(f) cout << "YES"<<endl;
  else cout << "NO"<<endl;
}
int N,M;
const int MAX_V = 10000;
vector<vector<ll>> cost;
ll mincost[MAX_V];
bool used[MAX_V];
ll V;

ll Prim(){
  for(ll i = 0; i < V; ++i){
    mincost[i] = inf;
    used[i] = false;
  }
  mincost[0] = 0;
  ll res =0;

  while(1){
    int v = -1;
    for(ll u = 0; u < V; ++u){
      if( !used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
    }

    if( v == -1){
      break;
    }
    used[v] = true;
    res += mincost[v];
    for(ll u = 0; u < V; ++u){
      mincost[u] = min(mincost[u],cost[v][u]);
    }
  }
  return res;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  while(cin >> N >> M && N && M){
    ll a,b,c;
    V = N;
    cost = vector<vector<ll>>(V,vector<ll>(V,inf));
    rep(i,M){
      cin >> a >> b >> c;
      cost[a][b] = c;
      cost[b][a] = c;
    }
    cout << Prim() << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG false

#define MAX_V 100
#define INF INT_MAX

int cost[MAX_V][MAX_V];
int mincost[MAX_V];
bool used[MAX_V];
int V;

int prim(){
    for(int i=0;i<V;++i){
        mincost[i]=INF;
        used[i]=false;
    }
    mincost[0]=0;
    int res=0;
    while(true){
        int v=-1;
        rep(u,V){
            if(!used[u] && (v==-1 || mincost[u] <mincost[v])) v=u;
        }
        if(v==-1) break;
        used[v]= true;
        res+=mincost[v];
        rep(u,V){
            mincost[u]=min(mincost[u],cost[v][u]);
        }
    }
    return res;
}
int main(){
    int n,m;
    while(cin>>n>>m){
        if(n==0&&m==0){
            break;
        }
        V=n;    
    rep(i,MAX_V){
        rep(j,MAX_V){
            cost[i][j]=INF;
        }
    }
    int a,b,c;
    rep(i,m){
        cin>>a>>b>>c;
        cost[a][b]=c;
        cost[b][a]=c;
    }
    cout<<prim()<<endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;

int n, m;
vector<P> branch[128];

int prim();

int main()
{
    while (scanf("%d %d", &n, &m), n != 0){
        for (int i = 0; i < n; i++) branch[i].clear();

        for (int i = 0; i < m; i++){
            int a, b, c;

            scanf("%d %d %d", &a, &b, &c);
            branch[a].push_back(P(c, b));
            branch[b].push_back(P(c, a));
        }
        printf("%d\n", prim());
    }

    return 0;
}

int prim()
{
    bool v[1024] = {false};
    priority_queue<P, vector<P>, greater<P> > q;
    int sum = 0;

    q.push(P(0, 0));
    v[0] = 0;
    while (!q.empty()){
        P p = q.top(); q.pop();

        if (v[p.second]) continue;
        v[p.second] = true;
        sum += p.first;
        for (int i = 0; i < branch[p.second].size(); i++){
            q.push(branch[p.second][i]);
        }
    }

    return sum;
}