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
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <tuple>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<vector<PII> > VVPII;
typedef priority_queue<PII, vector<PII>, greater<PII> > PQPII;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define MT make_tuple
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);
const int DX[] = {0, 1, 0, -1};
const int DY[] = {-1, 0, 1, 0};

//other
//--------------------------------------------
#define RANGE(a, c, b) ((a <= b) && (b < c))

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const int INF = (int) 10e9;

int solve(int n, int m){
	VVPII node(n);
	int from, to, cost;
	REP(i, m){
		cin >> from >> to >> cost;
		node[from].PB(MP(cost, to));
	}
	PQPII q;
	VI costs(n, INF);
	costs[0] = 0;
	q.emplace(0, 0);
	int result = 0;
	while(!q.empty()){
		int w = q.top().first, u = q.top().second; q.pop();
		if(costs[u] < w) continue;
		result += w;
		for(PII p : node[u]){
			if(p.first < costs[p.second]){
				costs[p.second] = p.first;
				q.emplace(p.first, p.second);
			}
		}
	}
	return result;
}

int main(int argc, char const *argv[])
{
	for(int n, m; cin >> n >> m, n | m;){
		cout << solve(n, m) << endl;
	}
	
	return 0;
}

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

class UnionFind
{
private:
  vector<int> parent, rank;

public:
  UnionFind(int n)
  {
    for (int i = 0; i < n; ++i) {
      parent.push_back(i);
      rank.push_back(0);
    }
  }

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

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

    if (rank[x] < rank[y]) {
      parent[x] = y;
    } else {
      parent[y] = x;
      if (rank[x] == rank[y])
	++rank[x];
    }
  }

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

int main()
{
  int n, m;
  while (cin >> n >> m) {
    if ((n|m) == 0)
      break;

    priority_queue<pair<int, pair<int, int> >, vector<pair<int, pair<int, int> > >, greater<pair<int, pair<int, int> > > > que;
    for (int i = 0; i < m; ++i) {
      pair<int, pair<int, int> > p;
      cin >> p.second.first >> p.second.second >> p.first;
      que.push(p);
    }

    int ans = 0;
    UnionFind uf(n);
    while (!que.empty()) {
      const pair<int, pair<int, int> > p = que.top();
      que.pop();

      if (!uf.same(p.second.first, p.second.second)) {
	uf.unite(p.second.first, p.second.second);
	ans += p.first;
      }
    }

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

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

#define MAXV 100
#define INF 100000000

int cost[MAXV][MAXV];
int mincost[MAXV];
bool used[MAXV];
int V;

int prim(){
	for(int i=0;i<V;++i){
		mincost[i]=INF;
		used[i]=false;
	}
	mincost[0]=0;
	int res=0;

	while(true){
		int v=-1;
		for(int u=0;u<V;u++){
			if(!used[u]&&(v==-1||mincost[u]<mincost[v])) v=u;
		}

		if(v==-1) break;
		used[v]=true;
		res+=mincost[v];

		for(int u=0;u<V;u++){
			mincost[u]=min(mincost[u],cost[v][u]);
		}
	}
	return res;
}

int main(){
     
	int m;
	int a,b,cot;

	while(1){
		 cin>>V>>m;
		 if(V==0&&m==0) break;
	
		  for(int i=0;i<V;i++){
			   for(int j=0;j<V;j++){
				   cost[i][j]=INF;
			   }
		   }

		   for(int i=0;i<m;i++){
			   cin>>a>>b>>cot;
			   cost[a][b]=cot;
			   cost[b][a]=cot;
		   }

		   cout<<prim()<<endl;
	  }

	 return 0;
}