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<cmath>
#include<cctype>
#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<deque>
#include<string>
#include<queue>
#include<map>
#include<set>
#include<utility>
#include<queue>

const int MAXN = 105;
using namespace std;

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }
  bool unionSet(int x, int y) {
    x = root(x); y = root(y);
    if (x != y) {
      if (data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) {
    return root(x) == root(y);
  }
  int root(int x) {
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x) {
    return -data[root(x)];
  }
};

struct edge{
  edge(int from,int to):from(from),to(to){}
  int from,to;
};

bool operator<(edge a,edge b){
  if(a.from != b.from)return a.from < b.from;
  else return a.to < b.to;
}

typedef pair<int,edge> P;

int main(){
  int n,m;
  while(cin >> n >> m && (n | m) != 0){
    priority_queue<pair<int,pair<int,int> > > que;
    for (int i = 0; i < m; ++i){
      int a,b,c;
      cin >> a >> b >> c;
      que.push(make_pair(c,make_pair(a, b)));
    }
    UnionFind u(MAXN);
    int ans = 0;
    for (int i = 0; i < m; ++i){
      int from = que.top().second.first;
      int to = que.top().second.second;
      int cost = que.top().first;
      if(!u.findSet(to, from)){
	//cout << "cost:" << cost << " " << top.to << " " << top.from << endl;
	ans += cost;
	u.unionSet(to,from);
      }
    }
    cout << ans << endl;
  }
  return 0;
}

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

int n, m;
int field[100][100];
bool used[100];

int prim() {
	// コスト、ノード番号
	typedef pair<int, int> edge;
	int result = 0;
	fill(used, used + n, false);
	priority_queue<edge, vector<edge>, greater<edge> > que;
	que.push(make_pair(0, 0));
	while (!que.empty()) {
		edge current = que.top();
		que.pop();
		int cost = current.first;
		int pos = current.second;
		if (used[pos]) continue;
		used[pos] = true;
		result += cost;
		for (int i = 0; i < n; i++) {
			if (field[pos][i] > 0 && !used[i]) {
				que.push(make_pair(field[pos][i], i));
			}
		}
	}
	return result;
}

int main() {
	while (cin >> n >> m, n || m) {
		memset(field, 0, sizeof(field));
		for (int i = 0; i < m; i++) {
			int a, b, c;
			cin >> a >> b >> c;
			field[a][b] = field[b][a] = c;
		}
		cout << prim() << endl;
	}
	return 0;
}

C++: #include <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
using namespace std;
#define INF 100000000
typedef long long ll;

int n, m;

// UnionFind
#define MAXN 110
int par[MAXN], rank[MAXN];

void init(int n_) {
    for (int i = 0; i < n_; i++) {
        par[i] = i;
        rank[i] = 0;
    }
}

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

// kruskal
#define MAXM 100010
struct edge {
    int from, to, cost;
};

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

edge es[MAXM];

int kruskal(void) {
    sort(es, es+m, comp);
    init(n);
    int ret = 0;
    for (int i = 0; i < m; i++) {
        edge e = es[i];
        if (!same(e.from, e.to)) {
            unite(e.from, e.to);
            ret += e.cost;
        }
    }
    return ret;
}
int main(void) {
    while (cin >> n >> m && n && m) {
        for (int i = 0; i < m; i++) {
            cin >> es[i].from >> es[i].to >> es[i].cost;
        }
        cout << kruskal() << endl;
    }
    return 0;
}