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<queue>
#include<vector>
#include<map>
#include<functional>
using namespace std;
int main()
{
	const int N = 100, INVALID_VALUE = 999;
	int cost[N][N],n,m,i,j,a,b,c,s;
	bool isUsed[N] = {false};

	while(scanf("%d%d",&n,&m),n)
	{
		for(i=0;i<n;++i)
		{
			for(j=0;j<n;++j) cost[i][j] = INVALID_VALUE;
			isUsed[i] = false;
		}
		for(i=0;i<m;++i) scanf("%d%d%d",&a,&b,&c), cost[a][b] = cost[b][a] = c;

		typedef pair<int,int>PII;	
		priority_queue<PII,vector<PII>,greater<PII> >q;
		PII p;
		q.push(make_pair(0,0));
		s = 0;
		while(!q.empty())
		{
			p = q.top(); q.pop();
			if(isUsed[p.second]) continue;
			isUsed[p.second] = true;
			s += p.first;

			for(i=0;i<n;++i)
			{
				c=cost[i][p.second];
				if(c!=INVALID_VALUE) q.push(make_pair(c,i));
			}
		}
		printf("%d\n",s);
	}
	return 0;
}

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

int cost[101][101];
int mincost[101];
bool used[101];
const int INF = 100000000;
int n,m;

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

  while(true) {
    int v = -1;
    for ( int u = 0; u < n; 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 < n; u++ ) {
      mincost[u] = min(mincost[u], cost[v][u]);
    }
  }
  return res;
}

int main() {
  while(cin >> n >> m, n||m) {
    for ( int i = 0; i < n; i++ ) {
      for ( int j = 0; j < n; j++ ) {
	cost[i][j] = INF;
      }
    }
    for (int i = 0; i < m; i++ ) {
      int a,b,c; cin >> a >> b >> c;
      cost[a][b] = cost[b][a] = c;
    }
    int ans = prim();
    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()){
            if(!used[G[from][i].to])
            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;
    }
}

C++: #include <cstdio>
#include <algorithm>

using namespace std;

//disjoint-set
int parent[100];

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

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

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

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

//graph
class Edge{
public:
  int cost,a,b;
  Edge(int c=0,int d=0,int e=0):cost(c),a(d),b(e){}
  bool operator< (const Edge& o) const {
    return cost < o.cost;
  }
};

//main
int n,m;
Edge graph[10000];

int main(){
  while(scanf("%d %d",&n,&m),n){
    for(int i=0; i<m; i++){
      int a,b,cost;
      scanf("%d %d %d",&a,&b,&cost);
      graph[i] = Edge(cost,a,b);
    }

    sort(graph,graph+m);

    int answer=0;
    init(n);

    for(int i=0; i<m; i++){
      Edge e = graph[i];
      if(!same_set_p(e.a,e.b)){
	answer += e.cost;
	unite(e.a,e.b);
      }
    }

    printf("%d\n",answer);
  }
}