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>
#define MAX 5010
using namespace std;

class edge{
public:
    int start;
    int goal;
    int cost;
    edge(){
        start = 0;
        goal = 0;
        cost = MAX;
    }
};
bool operator< (const edge &edge1, const edge &edge2){
    return edge1.cost < edge2.cost;
}
bool operator> (const edge &edge1, const edge &edge2){
    return edge1.cost > edge2.cost;
}

int P[101];
void init(int N){
    for(int i=0;i<=N;i++)
        P[i] = i;
}
int root(int a){
    if(P[a]==a)
        return a;
    return(P[a] = root(P[a]));
}
bool is_same_set(int a, int b){
    return root(a) == root(b);
}
void unit(int a, int b){
    P[root(a)] = root(b);
}

int main(){
    int n,m;
    while(cin >> n >> m && n!=0){
        init(n);
        int total = 0;
        vector<edge> v;
        for(int i=0;i<m;i++){
            edge tmp;
            cin >> tmp.start >> tmp.goal >> tmp.cost;
            v.push_back(tmp);
        }
        priority_queue<edge, vector<edge>, greater<edge> > p(v.begin(),v.end());
        for(int i=0;i<m;i++){
            edge tmp = p.top();
            p.pop();
            if(!is_same_set(tmp.start,tmp.goal)){
                total += tmp.cost;
                unit(tmp.start,tmp.goal);
            }
        }
        cout << total << endl;
    }
}

C++: #include <iostream>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <deque>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <functional>
#include <utility>
#include <algorithm>
#include <numeric>
#include <typeinfo>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <ctime>

using namespace std;

#define dump(n) cout<<"# "<<#n<<"="<<(n)<<endl
#define debug(n) cout<<__FILE__<<","<<__LINE__<<": #"<<#n<<"="<<(n)<<endl
#define repi(i,a,b) for(int i=int(a);i<int(b);i++)
#define rep(i,n) repi(i,0,n)
#define iter(c) __typeof((c).begin())
#define foreach(i,c) for(iter(c) i=(c).begin();i!=(c).end();i++)
#define allof(c) (c).begin(),(c).end()
#define mp make_pair

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int,int> pii;

struct Edge{
	int src,dst,weight;
	Edge(){}
	Edge(int src,int dst,int weight):src(src),dst(dst),weight(weight){}
};

bool operator<(const Edge& lhs,const Edge& rhs)
{
	return lhs.weight<rhs.weight;
}

bool operator>(const Edge& lhs,const Edge& rhs)
{
	return lhs.weight>rhs.weight;
}

typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

int Prim(Graph& g,Edges& tree,int root=0)
{
	tree.clear();
	
	int size=g.size();
	vector<int> visited(size);
	
	priority_queue<Edge,vector<Edge>,greater<Edge> > pq;
	pq.push(Edge(-1,root,0));
	int res=0;
	while(!pq.empty()){
		Edge e=pq.top();
		pq.pop();
		if(visited[e.dst])
			continue;
		if(e.src!=-1)
			tree.push_back(e);
		visited[e.dst]=1;
		res+=e.weight;
		rep(i,g[e.dst].size()){
			Edge cand=g[e.dst][i];
			if(!visited[cand.dst])
				pq.push(cand);
		}
	}
	return res;
}

int main()
{
	for(int n,m;cin>>n>>m,n|m;){
		Graph g(n);
		rep(i,m){
			int a,b,cost; cin>>a>>b>>cost;
			g[a].push_back(Edge(a,b,cost));
			g[b].push_back(Edge(b,a,cost));
		}
		
		Edges t;
		int res=Prim(g,t);
		cout<<res<<endl;
	}
	
	return 0;
}