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 <cstdio>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <queue>

using namespace std;

#define reep(i,f,t) for(int i=f ; i<int(t) ; ++i)
#define rep(i,n) reep(i, 0, n) 

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

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

	bool operator< (const Edge& e)const
	{
		return weight != e.weight ? weight > e.weight :
			src != e.src ? src < e.src : dst < e.dst;
	}
};

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

struct UnionFind
{
	vi data;

	UnionFind(int size) : data(size, -1) {}

	// xツづツづ個集ツ債づーツ閉ケツ債つキツづゥ
	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;
	}

	// xツづツづ個集ツ債つェツ督卍つオツつ「ツつゥツ偲ヲツ督セツつキツづゥ
	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)];
	}
};

pair<int, Edges> Kruskal(const Graph& g)
{
	int n = g.size();
	UnionFind uf(n);
	priority_queue<Edge> Q;

	rep(i, n) rep(j, g[i].size())
		if(i < g[i][j].dst)
			Q.push(g[i][j]);

	int total = 0;
	Edges F;
	while(F.size() < n-1 && !Q.empty()){
		Edge e = Q.top();
		Q.pop();
		if(uf.unionSet(e.src, e.dst)){
			F.push_back(e);
			total += e.weight;
		}
	}
	return pair<int, Edges>(total, F);
}

int main()
{
	int n, m;
	while(scanf("%d%d", &n, &m), n){
		Graph g(n);
		rep(i, m){
			int a, b, cost;
			scanf("%d%d%d", &a, &b, &cost);
			g[a].push_back(Edge(a, b, cost));
			g[b].push_back(Edge(b, a, cost));
		}

		pair<int, Edges> result = Kruskal(g);
		printf("%d\n", result.first);
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

class Edge {
public:
    int u, v, cost;
    Edge() {}
    Edge(int _u, int _v, int _cost) {
        u = _u;
        v = _v;
        cost = _cost;
    }

    bool operator<(const Edge& e) const {
        return cost < e.cost;
    }
};

class UnionFind {
public:
    int n;
    vector<int> parent_nodes, rank;
    UnionFind() {}
    UnionFind(int _n) {
        n = _n;
        // all node is same rank
        for (int i = 0; i < n; ++i) {
            parent_nodes.push_back(i);
            rank.push_back(0);
        }
    }

    int find(int v) {
        if(parent_nodes[v] == v) return v; // return root.
        return parent_nodes[v] = find(parent_nodes[v]); // compress path
    }

    // unite sets
    void unite(int x, int y) {
        x = find(x);
        y = find(y);

        if (x == y){
            return;
        }

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

        return;
    }

    // validation of same set
    bool same(int x, int y) {
        return find(x) == find(y);
    }
};

int kruskal(int n_vertex, int n_edge, vector<Edge> edges) {
    int costs = 0;
    sort(edges.begin(), edges.end());
    UnionFind uf = UnionFind(n_vertex);

    for (int i = 0; i < n_edge; ++i) {
        if(!uf.same(edges[i].u, edges[i].v)) {
            uf.unite(edges[i].u, edges[i].v);
            costs += edges[i].cost;
        }
    }

    return costs;
}


int main()
{
    int n, m, a, b, cost, result;
    vector<Edge> edges;
    while(cin>>n>>m) {
        if(n == 0 && m == 0) {
            break;
        }
        for (int i = 0; i < m; ++i) {
            cin >> a >> b >> cost;
            edges.push_back(Edge(a, b, cost));
        }

        result = kruskal(n, m, edges);
        cout << result << endl;
        edges.clear();
    }
    return 0;
}

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

struct bridge{
  int a;
  int b;
  int cost;
  bool operator<(const bridge &another) const{
    return cost<another.cost;
  };
};

int main(void){
  int n,m;
  int a,b,cost;
  int retval;
  while(1){
    cin>>n>>m;
    retval=0;
    if(n==0 and m==0)break;
    vector<bridge> bridges;
    for(int i=0;i<m;i++){
      bridge bri;
      cin>>a>>b>>cost;
      bri.a=a;
      bri.b=b;
      bri.cost=cost;
      bridges.push_back(bri);
    }
    sort(bridges.begin(),bridges.end());
    int city[n];
    for(int i=0;i<n;i++){
      city[i]=i;
    }
    for(int i=0;i<m;i++){
      bridge bri=bridges[i];
      if(city[bri.a]==city[bri.b]){
        continue;
      }
      else{
        retval+=bri.cost;
        int group=city[bri.b];
        for(int j=0;j<n;j++){
          if(city[j]==group){
            city[j]=city[bri.a];
          }
        }
      }
    }
    cout<<retval<<endl;
  }
  return 0;
}