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<stdio.h>
#include<cmath>
#define INF 9999999
using namespace std;
int n,m,t[100][100],a,b,c,d,flg[10],sum,mini,miniNo;
void prim(){
	int visited[100],mini,miniNo;
	int cost[100],pi[100];
	for(int i=0;i<n;i++){
		visited[i]=0;
		cost[i]=INF;
	}
	cost[0]=0;
	pi[0]=-1;
	while(1){
		mini=INF;
		for(int i=0;i<n;i++){
			if(mini>cost[i]&&visited[i]==0){
				miniNo=i;
				mini=cost[i];
			}
		}
		if(mini==INF)break;
		visited[miniNo]=1;
		for(int i=0;i<n;i++){
			if(t[miniNo][i]!=INF&&visited[i]==0){
				if(t[miniNo][i]<cost[i]){
					cost[i]=t[miniNo][i];
					pi[i]=miniNo;
				}
			}
		}
	}
	int total=0;
	for(int i=0;i<n;i++){
		if(pi[i]==-1)continue;
		total+=t[i][pi[i]];
	}
	cout<<total<<endl;
}
int main(){
	while(1){
		for(int i=0;i<100;i++){
			for(int j=0;j<100;j++){
				t[i][j]=INF;
			}
		}
		cin>>n>>m;
		if(n==0&&m==0)break;
		for(int i=0;i<m;i++){
			cin>>a>>b>>c;
			t[a][b]=t[b][a]=c;
		}
		prim();
	}
	return 0;
}

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

int n,m,sum;
int P[110],a[10010],b[10010],cost[10010];
pair<int,int> bridge[10010];
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]));
}

int main() {
	cin >> n >> m;
	while(n!=0 && m!=0) {
		for(int i=0; i<m; ++i) {
			cin >> a[i] >> b[i] >> cost[i];
			bridge[i].first = cost[i];
			bridge[i].second = i;
		}
		sort(bridge,bridge+m);
		init(n);
		for(int i=0; i<m; ++i) {
			if(P[b[bridge[i].second]] == b[bridge[i].second]) {
				if(P[a[bridge[i].second]] != b[bridge[i].second]) {
					P[b[bridge[i].second]] = a[bridge[i].second];
					root(b[bridge[i].second]);
					sum += bridge[i].first;
				}
			}
		}
		cout << sum << endl;
		cin >> n >> m;
		sum =0;
	}
}

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

class UnionFind {
private:
  int *par, *rank;

public:
  UnionFind() {}
  UnionFind(int n) {
    par = new int[n];
    rank = new int[n];
    for(int i = 0; i < n; ++i) {
      par[i] = i;
      rank[i] = 0;
    }
  }

  int find(int x) {
    if(par[x] == x) return x;
    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;
    if(rank[x] < rank[y]) {
      par[x] = y;
    } else {
      par[y] = x;
      if(rank[x] == rank[y]) {
        ++rank[x];
      }
    }
  }
};


int main() {
  int n, m;
  while(cin >> n >> m && (n|m)) {
    pair<int,pair<int,int> > es[m];
    for(int i = 0; i < m; ++i) {
      cin >> es[i].second.first
          >> es[i].second.second
          >> es[i].first;
    }
    sort(es, es+m);
    UnionFind uf(n);
    int res = 0;
    for(int i = 0; i < m; ++i) {
      int a = es[i].second.first;
      int b = es[i].second.second;
      if(!uf.same(a,b)) {
        res += es[i].first;
        uf.unite(a,b);
      }
    }
    cout << res << endl;
  }
  return 0;
}

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

class UnionFind {
public:
	UnionFind(size_t n) : parent(n, -1) {}

	void init(size_t n)
	{
		parent.assign(n, -1);
	}

	int root(int x)
	{
		int x_parent = parent[x];
		if (x_parent < 0)
		{
			return x;
		} else
		{
			return parent[x] = root(x_parent);
		}
	}

	bool unite(int x, int y)
	{
		int x_parent = root(x);
		int y_parent = root(y);
		if (x_parent == y_parent)
		{
			return false;
		} else if (x_parent < y_parent)
		{
			parent[x_parent] += parent[y_parent];
			parent[y_parent] = x_parent;
			return true;
		} else
		{
			parent[y_parent] += parent[x_parent];
			parent[x_parent] = y_parent;
			return true;
		}
	}

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

	int size(int x)
	{
		return -parent[root(x)];
	}

private:
	// negative(parent): num of members
	// positive(child) : parent index
	std::vector<int> parent;
};

struct Edge
{
	int a;
	int b;
	int cost;

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

int main()
{
	int n, m;
	int ans_sum;
	UnionFind uf(500);
	priority_queue<Edge> que;

	while (true)
	{
		cin >> n >> m;
		if (n == 0)
			return 0;

		ans_sum = 0;
		uf.init(m);
		que = priority_queue<Edge>();

		for (int i = 0; i < m; ++i)
		{
			int a, b, cost;
			cin >> a >> b >> cost;
			que.push(Edge{ a, b, cost });
		}

		while (!que.empty())
		{
			Edge e = que.top(); que.pop();
			if (uf.unite(e.a, e.b))
			{
				ans_sum += e.cost;
			}
		}
		cout << ans_sum << endl;
	}
}