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 <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <cfloat>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <fstream>
#include <functional>
#include <bitset>
#define chmin(a, b) ((a)=min((a), (b)))
#define chmax(a, b) ((a)=max((a), (b)))
#define fs first
#define sc second
#define eb emplace_back
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;

const ll MOD=1e9+7;
const ll INF=1e18;
const double pi=acos(-1);
const double eps=1e-10;

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

const int MAX_N = 110;

int par[MAX_N];
int ranks[MAX_N];
int ufSize;

void init(int n){
    ufSize = n;
    for(int i=0; i<n; i++){
        par[i] = i;
        ranks[i] = 0;
    }
}

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

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

void unite(int x, int y){
    x = find(x);
    y = find(y);
    if(x == y) return;
    ufSize--;

    if(ranks[x] < ranks[y]){
        par[x] = y;
    }
    else{
        par[y] = x;
    }
    
    if(ranks[x] == ranks[y]){
        ranks[x]++;
    }
}

int kruskal(int n, vector<T> &edge){
    sort(edge.begin(), edge.end());
    init(n);
    int res = 0;
    for(int i=0; i<edge.size(); i++){
        int cost, cv, nv;
        tie(cost, cv, nv) = edge[i];
        if(!same(cv, nv)){
            unite(cv, nv);
            res += cost;
        }
    }

    return res;
}

int main(){
    while(1){
        int n, m; cin>>n>>m;
        if(n == 0) return 0;
        vector<T> edge;
        for(int i=0; i<m; i++){
            int a, b, c; cin>>a>>b>>c;
            edge.eb(T(c, a, b));
        }

        cout << kruskal(n, edge) << endl;
    }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <cstring>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <stack>
#include <queue>

using namespace std;
typedef long long LL;
typedef pair<int, int> PII;
static const double EPS = 1e-5;

#define FOR(i,k,n) for (int i=(k); i<(int)(n); ++i)
#define REP(i,n) FOR(i,0,n)
int cost[100][100];
int mincost[100];
bool used[100];
const int INF = 1e6;
int main(void){
  int n,m;
  while(cin>>n>>m){
    if(n==0) break;
    REP(i,n){
      REP(j,n)cost[i][j] = INF;
      mincost[i]=INF;
      used[i] = false;
    }
    REP(i,m){
      int a,b,c;
      cin>>a>>b>>c;
      cost[a][b] = cost[b][a] = c;
    }
    mincost[0] = 0;
    int ans = 0;
    while(true){
      int v = -1;
      REP(u,n)
        if(!used[u]&&(v==-1||mincost[u]<mincost[v]))
          v = u;
      if(v==-1) break;
      ans += mincost[v];
      used[v] = true;
      REP(u,n)mincost[u] = min(mincost[u],cost[v][u]);
    }
    cout<<ans<<endl;
  }

  return 0;
}

C++: #include <iostream>
#include <vector>
#include <cstring>
#include <queue>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
using namespace std;

const int INF = 100000000;

struct edge {
    int to, cost;
    bool operator<(const edge& r)const{
        return cost>r.cost;
    }
};

// state = edge
// struct state {
//     int from, d;
// };
vector<vector<edge> > G;
int V;

bool used[111];
int prim(){
    int sum=0;
    int es=0;
    memset(used,0,sizeof(used));
    priority_queue<edge> q;
    q.push({0,0});
    while(es!=G.size()){
        edge e=q.top(); q.pop();
        if(used[e.to])continue;
        es++;
        used[e.to]=1;
        int from=e.to;
        //cout<<" "<<from<<endl;
        sum+=e.cost;
        FOR(i,0,G[from].size()){
            q.push(G[from][i]);
        }
    }
    return sum;
}

int main(){
    int m;
    while(1){
        cin>>V>>m;
        if(!(m||V))break;
        G=vector<vector<edge> >(V);
        FOR(i,0,m){
            int a,b,cost;cin>>a>>b>>cost;
            G[a].push_back({b,cost});
            G[b].push_back({a,cost});
        }
        cout<<prim()<<endl;
    }
}