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 <algorithm>
using namespace std;

struct Dset {
  Dset *parent;
  int rank;

  Dset() {
    clear();
  }

  void clear() {
    parent = NULL;
    rank = 0;
  }

  Dset *find() {
    if (!parent) {
      return this;
    } else {
      parent = parent->find();
      return parent;
    }
  }

  bool merge(Dset *a) {
    Dset *myRoot = find();
    Dset *yourRoot = a->find();
    if (myRoot->rank < yourRoot->rank) {
      myRoot->parent = yourRoot;
    } else if (myRoot->rank > yourRoot->rank) {
      yourRoot->parent = myRoot;
    } else if (myRoot != yourRoot) {
      yourRoot->parent = myRoot;
      myRoot->rank++;
    } else {
      return false;
    }
    return true;
  }
};

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

int main() {
  int n, m, ans;
  Bridge bridge[100];
  Dset x[100];
  while (1) {
    cin >> n >> m;
    if (!n && !m) break;
    for (int i=0; i<m; i++) {
      cin >> bridge[i].a >> bridge[i].b >> bridge[i].cost;
    }
    sort(bridge, bridge+m);
    for (int i=0; i<m; i++) {
      x[i].clear();
    }
    ans = 0;
    for (int i=0; i<m; i++) {
      if (x[bridge[i].a].merge(&x[bridge[i].b])) {
        ans += bridge[i].cost;
      }
    }
    cout << ans << endl;
  }

  return 0;
}

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

#define loop(i, n) for (int i = 0; i < n; i++) 
#define INF 1010001000

typedef pair<int, int> i_i;
typedef struct Edge{ int fr, to, co; } Edge;

int n, m;
int par[101], rank[101];

void init(int n);
int find(int x);
void unite(int x, int y);
bool same(int x, int y);
int kruskal(Edge e[]);
bool cmp(const Edge &e1, const Edge &e2);

int main()
{
    while (cin >> n >> m, (n|m)) {
        Edge e[m];
        loop(i, m) {
            cin >> e[i].fr >> e[i].to >> e[i].co;
        }
        cout << kruskal(e) << endl;
    }
    return 0;
}

int kruskal(Edge e[])
{
    sort(e, &e[m], cmp);
    int ans = 0;
    init(n);
    loop(i, m) {
        if (!same(e[i].fr, e[i].to)) {
            ans += e[i].co;
            unite(e[i].fr, e[i].to);
        }
    }
    return ans;
}

void init(int n)
{
    loop(i, n) {
        par[i] = i;
        rank[i] = 0;
    }
}

int find(int x)
{
    if (par[x] == x) {
        return x;
    } else {
        return par[x] = find(par[x]);
    }
}

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]++;
        }
    }
}

bool same(int x, int y)
{
    return find(x) == find(y);
}
                
bool cmp(const Edge &e1, const Edge &e2)
{
    return e1.co < e2.co;
}

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

struct Edge {
  int from, to, cost;
  Edge() : from(0), to(0), cost(0) { }
  Edge(int from, int to, int cost) : from(from), to(to), cost(cost) { }
};

struct UnionFind {
  vector<int> data;

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

  bool same(int i, int j) {
    return root(i) == root(j);
  }

  int root(int i) {
    return data[i] < 0 ? i : data[i] = root(data[i]);
  }

  void join(int i, int j) {
    data[root(i)] += data[root(j)];
    data[root(j)] = root(i);
  }
};

int main() {
  for(int n, m; cin >> n >> m && n; ) {
    vector<Edge> edges(m);

    for(int i = 0; i < m; i++) {
      cin >> edges[i].from >> edges[i].to >> edges[i].cost;
    }

    sort(edges.begin(), edges.end(), [](const Edge& a, const Edge& b) {
      return a.cost < b.cost;
    });

    int cost = 0;
    UnionFind uf(n);

    for(auto it = edges.begin(); it != edges.end(); it++) {
      if(!uf.same(it->from, it->to)) {
        uf.join(it->from, it->to);
        cost += it->cost;
      }
    }

    cout << cost << endl;
  }
}