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 <string>
#include <vector>
#include <iterator>
#include <sstream>
using namespace std;

vector<int> input(size_t n){
	string s;
	if(!getline(cin, s)){ throw 0; }
	stringstream ss1(s), ss2;
	istream_iterator<int> beg(ss1), en;
	vector<int> ret(beg, en);
	if(ret.size() != n){ throw 0; }
	for(size_t i = 0; i < n; ++i){
		if(i){ ss2 << ' '; }
		ss2 << ret[i];
	}
	if(ss2.str() != s){ throw 0; }
	return ret;
}

int main(){
	while(1){
		vector<int> v = input(2);
		int n = v[0], m = v[1];
		if(n == 0 && m == 0){ break; }
		if(n < 2 || n > 100){ throw 0; }
		for(int i = 0; i < m; ++i){
			v = input(3);
			int a = v[0], b = v[1], c = v[2];
			if(a < 0 || a >= n || b < 0 || b >= n){ throw 0; }
			if(c < 1 || c > 100){ throw 0; }
		}
	}
	if(cin.eof()){ throw 0; }
	cin.peek();
	if(!cin.eof()){ throw 0; }
}

C++: #define _USE_MATH_DEFINES
#define INF 10000000
#include <iostream>
#include <sstream>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>
#include <limits>
#include <map>
#include <string>
#include <cstring>
#include <set>
#include <deque>
#include <bitset>

using namespace std;

typedef long long ll;
typedef pair<int,string> P;

static const double eps = 1e-8;

int path[101][101];

int main(){
	string str;
	int n,m;
	while(~scanf("%d %d",&n,&m)){
		if(n==m && m==0) continue;
		
		int* mincost = new int[n];
		bool* used = new bool[n];

		fill((bool*)used,(bool*)used + n,false);
		fill((int*)mincost,(int*)mincost+n,INF);
		fill((int*)path,(int*)path+101*101,INF);

		for(int i=0;i<m;i++){
			int a,b,cost;
			scanf("%d %d %d",&a,&b,&cost);
			path[a][b] = min(cost,path[a][b]);
			path[b][a] = min(cost,path[b][a]);
		}

		int res=0;
		mincost[0] = 0;

		while(1){
			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],path[v][u]);
			}
			
		}

		printf("%d\n",res);

		delete[] mincost;
		delete[] used;
	}
}

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

#define MAX_N 1000

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

#define MAX_E 1000
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<vector>
#include<algorithm>
using namespace std;

int n, m;

class DisjointSet{
  public:
    vector<int> rank, p;

    DisjointSet(){}
    DisjointSet(int size){
        rank.resize(size, 0);
        p.resize(size, 0);
        for(int i = 0; i < size; i++) makeSet(i);
    }

    void makeSet(int x){
        p[x] = x;
        rank[x] = 0;
    }

    bool same(int x, int y){
        return findSet(x) == findSet(y);
    }
    
    bool unite(int x, int y){
        link(findSet(x), findSet(y));
    }

    void link(int x, int y){
        if(rank[x] > rank[y]){
            p[y] = x;
        }else{
            p[x] = y;
            if(rank[x] == rank[y]){
                rank[y]++;
            }
        }
    }

    int findSet(int x){
        if(x != p[x]){
            // path compression
            p[x] = findSet(p[x]);
        }
        return p[x];
    }
};

struct bridge{
    int from, to, cost;
    bridge(int f, int t, int c) : from(f), to(t), cost(c) {}
    bool operator<(const bridge other) const{
        return cost < other.cost;
    }
};

int main(){
    while(1){
        cin >> n >> m;
        if(n+m == 0)  break;

        DisjointSet uf(n);
        int a, b, c;
        vector<bridge> vb; 
        for(int i = 0; i < m; i++){
            cin >> a >> b >> c;
            vb.push_back(bridge(a,b,c));
        }

        sort(vb.begin(), vb.end());

        int ans = 0;
        for(bridge b : vb){
            if(uf.same(b.from, b.to))   continue;

            ans += b.cost;
            uf.unite(b.from, b.to);
        }

        cout << ans << endl;
    }
    return 0;
}