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 <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)

const int INF = 1 << 24;
const int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};

typedef unsigned long long ull;

int N, M;
int cost[110][110];

int prim(){
    int mincost[110], used[110];
    REP(i, 110){
        mincost[i] = INF;
        used[i] = 0;
    }

    mincost[0] = 0;
    
    int res = 0;
    while(1){
        int u = -1;
        
        REP(i, N){
            if(!used[i] && (u == -1 || mincost[u] > mincost[i])){u = i;}
        }

        if(u == -1){break;}

        used[u] = 1;
        res += mincost[u];

        REP(i, N){
            mincost[i] = std::min(mincost[i], cost[i][u]);
        }
    }

    return res;
}

int main(){
    while(std::cin >> N >> M, N){
        REP(i, 110){
            REP(j, 110){
                cost[i][j] = INF;
            }
        }

        REP(i, M){
            int to, from, co;
            std::cin >> to >> from >> co;

            cost[to][from] = co;
            cost[from][to] = co;
        }

        std::cout << prim() << std::endl;
    }
}

C++: #include<cmath>
#include<cctype>
#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
#include<deque>
#include<string>
#include<queue>
#include<map>
#include<set>
#include<utility>
#include<queue>

const int MAXN = 105;
using namespace std;
struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) { }
  bool unionSet(int x, int y) {
    x = root(x); y = root(y);
    if (x != y) {
      if (data[y] < data[x]) swap(x, y);
      data[x] += data[y]; data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) {
    return root(x) == root(y);
  }
  int root(int x) {
    return data[x] < 0 ? x : data[x] = root(data[x]);
  }
  int size(int x) {
    return -data[root(x)];
  }
};
struct edge{
  edge(int from,int to):from(from),to(to){}
  int from,to;
};
bool operator<(edge a,edge b){
  if(a.from != b.from)return a.from < b.from;
  else return a.to < b.to;
}
typedef pair<int,edge> P;

int main(){
  int n,m;

  while(cin >> n >> m && n + m != 0){
    priority_queue<pair<int,edge>,vector<P>,greater<P> > que;
    for (int i = 0; i < m; ++i){
      int a,b,c;
      cin >> a >> b >> c;
      que.push(make_pair(c,edge(a,b)));
    }

    UnionFind u(m);
    int cost = 0;
    for (int i = 0; i < n-1; ++i){
      edge top = que.top().second;
      int topCost = que.top().first;
      que.pop();
      if(u.unionSet(top.from,top.to)){
	cost += topCost;
	cout << "cost:" << topCost << " " << top.from << "," <<top.to << endl;
      }
    }
    cout << cost << endl;
  }
  return 0;
}

C++: #include <vector>
#include <map>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define rep(i,n) for(int i=0;i<(int)(n);i++)
const int INF = 10000000;

using namespace std;
/** Problem0180 : Stellar Performance of the Debunkey Family **/
int cost[100][100];
int mincost[100];
bool used[100];
int V, E;

int prim()
{
	for (int i=0; i<V; i++) {
		mincost[i] = INF;
		used[i] = false;
	}
	mincost[0]=0;
	int res=0;
	
	while (1) {
		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()
{
	while (cin >> V >> E, V!=0 && E!= 0) {
		rep(i, 100) rep(j, 100) cost[i][j]=INF;
		
		rep(i, E) {
			int a, b, c;
			cin >> a >> b >> c;
			cost[a][b] = c;
			cost[b][a] = c;
		}
		cout << prim() << endl;
	}
	return 0;
}

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

int n, m;

const int UFSIZE = 110;
int P[UFSIZE]; // 親

void init() {
  for (auto i=0; i<n; i++) {
    P[i] = i;
  }
}

int root(int a) {
  if (a == P[a]) return a;
  return (P[a] = root(P[a]));
}

bool issame(int a, int b) {
  return root(a) == root(b);
}

void unite(int a, int b) {
  P[root(a)] = root(b);
}


int main() {
  while (cin >> n >> m && n) {
    vector< tuple<int, int, int> > V; // cost, node1, node2
    for (auto i=0; i<m; i++) {
      int a, b, cost;
      cin >> a >> b >> cost;
      V.push_back(make_tuple(cost, a, b));
    }
    sort(V.begin(), V.end());
    int sum = 0;
    init();
    for (auto i=0; i<m; i++) {
      int cost = get<0>(V[i]);
      int nodea = get<1>(V[i]);
      int nodeb = get<2>(V[i]);
      if (!issame(nodea, nodeb)) {
	unite(nodea, nodeb);
	sum += cost;
      }
    }
    cout << sum << endl;
  }
}