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 <iostream>
#include <queue>
#include <vector>

using namespace std;

class Bridge
{
public:
	int from;
	int to;
	int cost;

	Bridge() : from(0), to(0), cost(0) {}

	bool operator > (const Bridge& b) const
	{
		return cost > b.cost;
	}

	bool operator < (const Bridge& b) const
	{
		return cost < b.cost;
	}
};



int nCity, nBridge;

Bridge bridge[100];
bool city[100];

int main()
{
	while( 1 )
	{
		//load data
		cin >> nCity >> nBridge;
		if(nCity == 0 && nBridge == 0)
		{
			break;
		}

		for(int i=0; i<nBridge; i++)
		{
			cin >> bridge[i].from >> bridge[i].to >> bridge[i].cost;
		}

		for(int i=0; i<nCity; i++)
		{
			city[i] = false;
		}

		//set initial node to queue
		priority_queue<Bridge, vector<Bridge>, greater<Bridge> > que;
		for(int i=0; i<nBridge; i++)
		{
			if(bridge[i].from == 0 || bridge[i].to == 0)
			{
				que.push(bridge[i]);
			}
		}

		city[0] = true;

		//iteration
		int totalCost = 0;
		while(!que.empty())
		{
			//end check
			bool isEnd = true;
			for(int i=0; i<nCity; i++)
			{
				if(!city[i])
				{
					isEnd = false;
					break;
				}
			}

			if(isEnd)
			{
				break;
			}

			//check highest priority node
			Bridge current = que.top();
			que.pop();

			totalCost += current.cost;

			int next = 0;
			if(!city[current.to])
			{
				city[current.to] = true;
				next = current.to;
			}
		
			if(!city[current.from])
			{
				city[current.from] = true;
				next = current.from;
			}

			for(int i=0; i<nBridge; i++)
			{
				if(bridge[i].to == next || bridge[i].from == next)
				{
					if(!city[bridge[i].to] || !city[bridge[i].from])
					{
						que.push(bridge[i]);
					}
				}
			}
		}

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

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

#define MAX_N 101
#define MAX_E 1001

struct Edge {
  int u, v, cost;
};
int par[MAX_N], rank[MAX_N];
Edge es[MAX_E];

int V, E;

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

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

bool issame(int x, int y) {
  return p_find(x) == p_find(y);
}

void unite(int x, int y) {
  x = p_find(x);
  y = p_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 comp(const Edge &e1, const Edge &e2) {
  return e1.cost < e2.cost;
}

int kruskal() {
  sort(es, es+E, comp);
  init_union_find();
  int res = 0;
  for(int i=0; i<E; i++) {
    Edge e = es[i];
    if(!issame(e.u, e.v)) {
      unite(e.u, e.v);
      res += e.cost;
    }
  }
  return res;
}

int main() {
  while(cin >> V >> E && V+E) {
    for(int i=0; i<E; i++) {
      cin >> es[i].u >> es[i].v >> es[i].cost;
    }
    cout << kruskal() << endl;
  }
  
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll=long long;
using vin=vector<int>;
using vll=vector<long long>;
using vvin=vector<vector<int>>;
using vvll=vector<vector<long long>>;
using vstr=vector<string>;
using vvstr=vector<vector<string>>;
using vch=vector<char>;
using vvch=vector<vector<char>>;
using vbo=vector<bool>;
using vvbo=vector<vector<bool>>;
using vpii=vector<pair<int,int>>;
using pqsin=priority_queue<int,vector<int>,greater<int>>;
#define mp make_pair
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,s,n) for(int i=(s);i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define decp(n) cout<<fixed<<setprecision((int)n)
const int inf=1e9+7;
const ll INF=1e18;

vin par(200);
vin deep(200);
void init(int n);
int root(int x);
void unite(int x,int y);
bool same(int x,int y);
int a,b,c,res;

int kruskal(int n,int m){
    vector<tuple<int,int,int>> edge;
    rep(i,m){
        cin>>a>>b>>c;
        edge.push_back(make_tuple(c,a,b));
    }
    sort(all(edge));
    init(n);
    res=0;
    for(auto e:edge){
        if(!same(get<1>(e),get<2>(e))){
            unite(get<1>(e),get<2>(e));
            res+=get<0>(e);
        }
    }
    return res;
}

int main(){
    int n,m;
    queue<int> ans;
    while(1){
        cin>>n>>m;
        if(n==0&&m==0)break;
        ans.push(kruskal(n,m));
    }
    while(ans.size()){
        cout<<ans.front()<<endl;
        ans.pop();
    }
}

void init(int n){
    rep(i,n+1){
        par[i]=i;
        deep[i]=0;
    }
}
int root(int x){
    if(par[x]==x)return x;
    else return par[x]=root(par[x]);
}
void unite(int x,int y){
    x=root(x);
    y=root(y);
    if(x==y)return;
    if(deep[x]<deep[y])par[x]=y;
    else{
        par[y]=x;
        if(deep[x]==deep[y])deep[x]++;
    }
}
bool same(int x,int y){
    return root(x)==root(y);
}