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<stdio.h>
#include<algorithm>
using namespace std;
int UF[100];
pair<int,pair<int,int> > edge[10000];
int FIND(int a){
	if(UF[a]<0)return a;
	return UF[a]=FIND(UF[a]);
}
void UNION(int a,int b){
	a=FIND(a);
	b=FIND(b);
	if(a!=b){
		if(UF[a]<UF[b]){
			int val=a;
			a=b;
			b=val;
		}
		UF[b]+=UF[a];
		UF[a]=b;
	}
	return;
}
int main(){
	int a,b;
	while(scanf("%d%d",&a,&b),a){
		for(int i=0;i<a;i++)UF[i]=-1;
		for(int i=0;i<b;i++){
			int c,d,e;
			scanf("%d%d%d",&c,&d,&e);
			edge[i]=make_pair(e,make_pair(c,d));
		}
		std::sort(edge,edge+b);
		int ret=0;
		for(int i=0;i<b;i++){
			if(FIND(edge[i].second.first)!=FIND(edge[i].second.second)){
				ret+=edge[i].first;
				UNION(edge[i].second.first,edge[i].second.second);
			}
		}
		printf("%d\n",ret);
	}
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cmath>
#include <cassert>
#include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <numeric>
#include <complex>
#include <list>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <utility>
#include <functional>
#include <iterator>

using namespace std;

#define dump(n) cerr<<"# "<<#n<<"="<<(n)<<endl
#define repi(i,a,b) for(int i=int(a);i<int(b);i++)
#define peri(i,a,b) for(int i=int(b);i-->int(a);)
#define rep(i,n) repi(i,0,n)
#define per(i,n) peri(i,0,n)
#define iter(c) __typeof__((c).begin())
#define foreach(i,c) for(iter(c) i=(c).begin();i!=(c).end();++i)
#define all(c) (c).begin(),(c).end()
#define mp make_pair

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int,int> pii;

struct Edge{
	int src,dst,weight;
	Edge(){}
	Edge(int s,int d,int w):src(s),dst(d),weight(w){}
	bool operator<(const Edge& e)const{return weight<e.weight;}
	bool operator>(const Edge& e)const{return weight>e.weight;}
};
typedef vector<vector<Edge> > Graph;

int Prim(const Graph& g,vector<Edge>& tree,int root=0)
{
	tree.clear();
	
	vi vis(g.size());
	priority_queue<Edge,vector<Edge>,greater<Edge> > pq;
	pq.push(Edge(-1,root,0));
	int res=0;
	while(pq.size()){
		Edge cur=pq.top(); pq.pop();
		if(vis[cur.dst])
			continue;
		vis[cur.dst]=true;
		res+=cur.weight;
		if(cur.src!=-1)
			tree.push_back(cur);
		foreach(e,g[cur.dst])
			pq.push(*e);
	}
	return res;
}

int main()
{
	for(int n,m;scanf("%d%d",&n,&m),n|m;){
		Graph g(n);
		rep(i,m){
			int s,d,w; scanf("%d%d%d",&s,&d,&w);
			g[s].push_back(Edge(s,d,w));
			g[d].push_back(Edge(d,s,w));
		}
		
		vector<Edge> tree;
		int res=Prim(g,tree);
		printf("%d\n",res);
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define repb(i, a, b) for(int i = a; i >= b; i--)
#define all(a) a.begin(), a.end()
#define int long long
using namespace std;

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

bool cmp(data d1, data d2){
    return d1.cost < d2.cost;
}

struct UF{
    vector<int> par;
    vector<int> sz;
    void init(int n){
        par.resize(n);
        sz.resize(n, 1);
        rep(i, 0, n) par[i] = i;
    }
    int find(int x){
        if(x == par[x]) return x;
        return par[x] = find(par[x]);
    }
    void unite(int x, int y){
        x = find(x); y = find(y);
        if(x == y) return;
        if(sz[x] < sz[y]) swap(x, y);
        sz[x] += sz[y];
        par[y] = x;
    }
    bool same(int x, int y){
        return find(x) == find(y);
    }
};

signed main(){
    int n, m;
    while(1){
        cin >> n >> m;
        if(n + m == 0) break;
        vector<data> d(m);
        rep(i, 0, m){
            cin >> d[i].a >> d[i].b >> d[i].cost;
        }
        sort(all(d), cmp);
        UF uf;
        uf.init(n);
        int ans = 0;
        rep(i, 0, m){
            int u = d[i].a, v = d[i].b;
            if(!uf.same(u, v)){
                uf.unite(u, v);
                ans += d[i].cost;
            }
        }
        cout << ans << endl;
    }  
}