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 <sstream>
#include <fstream>

#include <ctime>
#include <cstdlib>
#include <cstring>
#include <cctype>

#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>

#include <cmath>
#include <algorithm>
#include <functional>
#include <numeric>

#define MAX_V 110
#define INF 1000000

using namespace std;

template<typename T> ostream& operator<<(ostream& os, const vector<T>& v){
    os << "{ ";
    for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
        os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", ");
    os << " }";
    return os;
}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<bool> vb;
typedef vector<vb> vvb;
#define vv(type,w,h,init) vector<vector<type>>(h,vector<type>(w,init))
typedef vector<string> vs;
typedef long long ll;
typedef unsigned uint;
typedef unsigned long ul;
typedef unsigned long long ull;

#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define loop(i,a,b) for(int i=(a); i<(int)(b); i++)
#define rep(i,b) loop(i,0,b)
#define pb push_back
#define mp make_pair

string const resstr[] = {"Impossible","Possible","No","Yes"};

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

int prom(){
	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];
		
		rep(u,V)
			mincost[u] = min(mincost[u], cost[v][u]);	
	}
	return res;
}

int main(){
	int E;
	while(cin >> V >> E, V+E){
		rep(i, V)
			rep(j, V) cost[i][j] = INF;
	
		rep(i, E){
			int a, b ,c;
			cin >> a >> b >> c;
			cost[a][b] = c;
			cost[b][a] = c;
		}
		cout << prom() << endl;
	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#define _w_ 1
const int INF=1e9;
int cost[101][101];
int mincost[101];
bool used[101];
int V;

int prim(){
	for(int i = 0; i < V; ++i){
		mincost[i]=INF;
		used[i]=false;
	}
	mincost[0]=0;
	int res=0;
	while(_w_){
		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] = std::min(mincost[u], cost[v][u]);
		}
	}
	return res;
}

int main(){
	int n, m;
	while(scanf("%d %d",&n, &m) , n+m){
		for(int i=0;i<101;++i){
			for(int j=0;j<101;++j){
				cost[i][j]=INF;
			}
		}

		for(int i=0;i<m;++i){
			int a, b, c;
			scanf("%d %d %d", &a, &b, &c);
			cost[a][b] = c, cost[b][a] = c;
		}
		V = n;
		printf("%d\n",prim());

	}
}

C++: #include<iostream>
#include<vector>
#include<cstdio>
#include<cmath>

#define REP(i,n) for(int i=0; i<(int)(n); i++)

using namespace std;

typedef unsigned long long ull;

int main(){
  int n,m;
  while(scanf("%d%d",&n,&m),n+m){
    int  cost[n][n];
    bool f[n];
    memset(cost, 0, sizeof(cost));
    memset(f, 0, sizeof(f));
    REP(i,m){
      int a,b,c;
      scanf("%d%d%d",&a,&b,&c);
      cost[a][b] = cost[b][a] = c;
    }
    f[0] = true;
    int ans = 0;
    REP(i,n-1){
      int m = INT_MAX;
      int ii,jj;
      for(int i=0; i<n; i++){
	for(int j=i+1; j<n; j++){
	  if(f[i] ^ f[j] && cost[i][j] != 0){
	    if(m > cost[i][j]){
	      ii = i; jj = j;
	      m = cost[i][j];
	    }
	  }
	}
      }
      f[ii] = f[jj] = true;
      ans += m;
    }

    printf("%d\n",ans);
  }
  return 0;
}

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

static const int INFTY = 1000001;
static const int MAX = 102;

class Edge{
public:
    int target, cost;
    Edge(int target = 0, int cost = 0) : target(target), cost(cost) {}
};

std::vector<Edge> G[MAX];
bool visited[MAX];
int parent[MAX], key[MAX];
int V, minv, min_index;

int minKey() {
    minv = INFTY;
    for (int v = 0; v < V; v++)
        if (!visited[v] && key[v] < minv)
            minv= key[v], min_index = v;
    return min_index;
}

void printMST()
{
    int sum = 0;
    for (int i = 1; i < V; i++)
        sum += key[i];
    std::printf("%d\n", sum);

}

void prim() {

    for (int i = 0; i < V; i++) {
        key[i] = INFTY;
        visited[i] = false;
    }
    key[0] = 0;
    parent[0] = -1;

    int current, target, cost;

    for (int i = 0; i < V-1; i++) {
        current = minKey();
        visited[current] = true;

        for (unsigned long v = 0; v < G[current].size(); v++) {
            target = G[current][v].target;
            cost = G[current][v].cost;
            if (!visited[target] && cost < key[target])
                parent[target] = current, key[target] = cost;
        }
    }
    printMST();

}


int main()
{
    int E, source, target, cost;
    for(; ;) {
        std::scanf("%d %d", &V, &E);
        if (V == 0 && E == 0) break;
        for (int i = 0; i < E; i++) {
            std::scanf("%d %d %d", &source, &target, &cost);
            G[source].push_back(Edge(target, cost));
            G[target].push_back(Edge(source, cost));
        }
        prim();
        for (int i = 0; i <= V; i++) G[i].clear();
    }
    return 0;
}