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 <cstdlib>
using namespace std;

struct Bridge
{
  int a, b, cost;
};

int n, m, ans, parent[10001];
Bridge bridge[10001];

int bridge_comp(const void *a, const void *b)
{
  return ((Bridge *)a)->cost - ((Bridge *)b)->cost;
}

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

int main()
{
  while((cin >> n >> m), n && m)
  {
    for (int i = 0; i < n; i++)
      parent[i] = i;
    for (int i = 0; i < m; i++)
      cin >> bridge[i].a >> bridge[i].b >> bridge[i].cost;
    qsort(bridge, m, sizeof(Bridge), bridge_comp);
    ans = 0;
    for (int i = 0; i < m; i++)
    {
      if ((n = root(bridge[i].a)) != root(bridge[i].b))
      {
	parent[root(bridge[i].b)] = n;
	ans += bridge[i].cost;
      }
    }
    cout << ans << endl;
  }
  return 0;
}

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

#define MAX_N 100

int par[MAX_N];
int rank[MAX_N];

#define MAX_E 100
struct edge { int u, v, cost; };
edge es[MAX_E];

int V, E;

void init_union_find(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;
  } 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 comp(const edge& e1, const edge& e2) {
  return e1.cost < e2.cost;
}

int kruskal() {
  sort(es, es + E, comp);
  init_union_find(V);
  int res = 0;
  for(int i=0; i<E; i++) {
    edge e = es[i];
    if(!same(e.u, e.v)) {
      unite(e.u, e.v);
      res += e.cost;
    }
  }
  return res;
}

int main() {

  while(cin >> V >> E && (V||E)) {
    for(int i=0; i<E; i++) {
      int a, b, c;
      cin >> a >> b >> c;
      es[i].u = a, es[i].v = b, es[i].cost = c;
    }
    cout << kruskal() << endl;
  }
  
  return 0;
}

C++: #include <iostream>
#include <bitset>
#include <vector>
#include <queue>
#include <limits.h>
using namespace std;

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

struct Bridge {
	int a, b, cost;
};

bool operator <(const Bridge& b1, const Bridge& b2) {
	return b1.cost < b2.cost;
}

bool operator >(const Bridge& b1, const Bridge& b2) {
	return b1.cost > b2.cost;
}

int n, m, a, b, cost;
const int MAX_N = 100;
int T[MAX_N][MAX_N];
priority_queue<Bridge, vector<Bridge>, greater<Bridge> > q;

int main() {
	while(cin >> n >> m, n | m) {
		fill(&T[0][0], &T[0][0]+MAX_N*MAX_N, INT_MAX);
		rep(i,m) {
			cin >> a >> b >> cost;
			T[a][b] = T[b][a] = cost;
		}

		q = priority_queue<Bridge, vector<Bridge>, greater<Bridge> >();
		rep(i,n) {
			if(T[0][i] != INT_MAX) {
				Bridge bdg;
				bdg.a = 0;
				bdg.b = i;
				bdg.cost = T[0][i];
				q.push(bdg);
			}
		}

		int total = 0;
		bitset<MAX_N> visited;
		visited.set(0);
		while(!q.empty()) {
			Bridge bdg = q.top();
			q.pop();
			if(visited[bdg.b]) continue;

			total += bdg.cost;
			visited.set(bdg.b);
			rep(i,n) {
				if(!visited[i] && T[bdg.b][i] != INT_MAX) {
					Bridge new_bdg;
					new_bdg.a = bdg.b;
					new_bdg.b = i;
					new_bdg.cost = T[bdg.b][i];
					q.push(new_bdg);
				}
			}
			
			if(visited.count() == n) break;
		}

		cout << total << endl;
	}
}