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>

#define rep(i, n) for (int i = 0; i < (n); i++)
#define REP(i, init, n) for (int i = init; i < (n); i++)

using namespace std;
using ll = long long int;
using P = pair<int, int>;
using T = tuple<int, int, int>;
using edge = struct
{
    int to, cost;
};

const int MOD = 1e9 + 7;
const int iINF = 1e9;
const long long int llINF = 1e18;
const double PI = acos(-1.0);

const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

class UnionFind
{
  private:
    vector<int> par;
    vector<int> sizes;

  public:
    UnionFind(int N) : par(N), sizes(N, 1)
    {
        rep(i, N) par[i] = i;
    }

    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 (sizes[x] < sizes[y])
            swap(x, y);

        par[y] = x;
        sizes[x] += sizes[y];
    }

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

    int size(int x)
    {
        return sizes[find(x)];
    }
};

int main()
{
    int N, M;
    while (cin >> N >> M, N)
    {
        vector<T> edges;

        rep(i, M)
        {
            int a, b, cost;
            cin >> a >> b >> cost;

            edges.push_back(make_tuple(cost, a, b));
        }

        sort(edges.begin(), edges.end());

        UnionFind uf(N);

        int ans = 0;

        for(auto e : edges)
        {
            int to, from, cost;
            tie(cost, to, from) = e;

            if(uf.same(from, to)) continue;

            uf.unite(from, to);

            ans += cost;

        }

        cout << ans << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <complex>
#include <sstream>
#include <string>
#include <algorithm>
#include <deque>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <vector>
#include <set>
#include <limits>
#include <cstdio>
#include <cctype>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <ctime>
using namespace std;
#define REP(i, j) for(int i = 0; i < (int)(j); ++i)
#define FOR(i, j, k) for(int i = (int)(j); i < (int)(k); ++i)
#define SORT(v) sort((v).begin(), (v).end())
#define REVERSE(v) reverse((v).begin(), (v).end())
typedef complex<double> P;

vector<int> v, parent, depth;

int find(int a){
  if(parent[a] == a) return a;
  else return parent[a] = find(parent[a]);
}

void merge(int a, int b){
  int pa = find(a), pb = find(b);
  if(pa == pb) return ;

  if(depth[pa] > depth[pb]) swap(pa, pb);
  if(depth[pa] == depth[pb]) ++depth[pa];
  parent[pb] = pa;
}

bool same(int a, int b){
  return find(a) == find(b);
}

void init_union_find(int V){
  v = vector<int>(V);
  parent = vector<int>(V);
  depth = vector<int>(V, 1);
  REP(i, V) parent[i] = i;
}

struct edge {
  int f, t, c;
  bool operator < (const edge &e) const { return c < e.c; };
};

int kruskal(int V, int E, vector<edge> es){
  sort(es.begin(), es.end());
  init_union_find(V);
  int min_cost = 0;
  REP(i, E){
    if(!same(es[i].f, es[i].t)){
      min_cost += es[i].c;
      merge(es[i].f, es[i].t);
    }
  }
  return min_cost;
}

int main() {
  int V, E;
  while(cin >>V >>E && V){
    vector<edge> es(E);
    REP(i, E) cin >>es[i].f >>es[i].t >>es[i].c;
    cout <<kruskal(V, E, es) <<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <set>
#include <algorithm>
#include <vector>

using namespace std;

int n, m;
vector< set< pair<int, int> > > cost(100,set< pair<int,int> >());

int prim()
{
	int res=0;
	set<int> v;
	v.insert(0);
	while(v.size()<n)
	{
		pair<int, int> mini(100000007, -1);
		for(set<int>::iterator it=v.begin();it!=v.end();it++)
		{
			for(set<  pair<int, int> >::iterator it2=cost[*it].begin();it2!=cost[*it].end();it2++)
				if(v.find((*it2).second)==v.end())
				{
					if(mini.first>(*it2).first)
						mini=(*it2);
					break;
				}
		}
		v.insert(mini.second);
		res+=mini.first;
	}
	return res;
}

int main()
{
	while(1)
	{
		cin >> n >> m;
		if(n==0&&m==0) break;
		for(int i=0;i<m;i++)
		{
			int a, b, c;
			cin >> a >> b >> c;
			cost[a].insert(pair<int, int>(c, b));
			cost[b].insert(pair<int, int>(c, a));
		}
		cout << prim() << endl;
		for(int i=0;i<m;i++)
			cost[i].clear();
	}
	return 0;
}