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 <utility>
#include <algorithm>
using namespace std;

int n,m,sum,r;
int P[110],a[10010],b[10010],cost[10010];
pair<int,int> bridge[10010];
void init(int N) {
	for(int i=0; i<N; ++i) P[i] = i;
}
int root(int a) {
	if(P[a] == a) return a;
	return (P[a] = root(P[a]));
}

int main() {
	cin >> n >> m;
	while(n!=0 && m!=0) {
		for(int i=0; i<m; ++i) {
			cin >> a[i] >> b[i] >> cost[i];
			bridge[i].first = cost[i];
			bridge[i].second = i;
		}
		sort(bridge,bridge+m);
		init(n);
		for(int i=0; i<m; ++i) {
			if(P[b[bridge[i].second]] != P[a[bridge[i].second]]) {
				if(P[a[bridge[i].second]] == a[bridge[i].second]) {
					P[a[bridge[i].second]] = P[b[bridge[i].second]];
					r = a[bridge[i].second];
				} else {
					P[b[bridge[i].second]] = P[a[bridge[i].second]];
					r = b[bridge[i].second];
				}
				for(int k=0; k<n; ++k) {
					if(P[k] == r) {
						root(k);
					}
				}
				sum += bridge[i].first;
				//}
			}
		}
		cout << sum << endl;
		cin >> n >> m;
		sum =0;
	}
}

C++: #include <stdio.h>
#define  MAX 101


struct Dis
{
    int pa[MAX];
    int used[MAX];
    int n;
    Dis(int n):n(n)
    {
        for(int i=0;i<n;i++)
        {
            pa[i]=i;
            used[i]=0;
        }
    }
    void use(int i)
    {
        used[i]=1;
    }
    int root(int a)
    {
        if(pa[a]==a)
            return a;
        return pa[a]=root(pa[a]);
    }
    bool is_same_set(int a,int b)
    {
        return root(a)==root(b);
    }
    void unite(int n,int m)
    {
        use(n);
        use(m);
        pa[root(n)]=root(m);
    }
    bool is_connected()
    {
        int rt=-1;
        for(int i=0;i<n;i++)
        {
            if(rt>=0 &&used[i] && rt!=root(i))
                return false;
            if(used[i])
                rt=root(i);
        }
        return rt!=-1;
    }
};

int br[6000][3];

int getMin(int m)
{
    int tmp=-1;
    for(int i=0;i<m;i++)
    {
        if(br[i][2]!=-1)
        {
            if(tmp==-1 || br[tmp][2]>br[i][2])
            {
                tmp=i;
            }
        }
    }
    if(tmp!=-1)
    {
        return tmp;
    }
    return -1;
}

int main(void)
{
    int n,m;
    while(scanf("%d%d",&n,&m)==2 && n && m)
    {
        Dis dis(n);
        for(int i=0;i<m;i++)
        {
            scanf("%d%d%d",br[i],br[i]+1,br[i]+2);
        }
        int nc=0;
        int cost=0;
        while(nc<n-1)
        {
            int min=getMin(m);
            if(min==-1)
            {
                puts("min=-1");
            }
            int a=br[min][0];
            int b=br[min][1];
            if(!dis.is_same_set(a,b))
            {
                dis.unite(a,b);
                nc++;
                cost+=br[min][2];
            }
            br[min][2]=-1;
        }
        printf("%d\n",cost);
    }
    return 0;
    
}

C++: #include <bits/stdc++.h>
#define int long long
using namespace std;


template<typename T>
struct Kruskal {
    struct Edge {
        int from, to;
        T cost;
        bool used;
        Edge(int from, int to, T cost) : from(from), to(to), cost(cost), used(false){}
        bool operator<(const Edge& e) const {
            return cost < e.cost;
        }
    };
    struct UF {
        vector<int> r, p;
        UF() = default;
        UF(int sz) : r(sz, 1), p(sz){ iota(begin(p), end(p), 0LL); }
        int find(int x){
            return (x == p[x] ? x : p[x] = find(p[x]));
        }
        bool same(int x, int y){
            return find(x) == find(y);
        }
        void unite(int x, int y){
            x = find(x), y = find(y);
            if(x == y) return;
            if(r[x] < r[y]) swap(x, y);
            r[x] += r[y];
            p[y] = x;
        }
    };
    vector<Edge> es;
    UF uf;
    Kruskal() = default;
    Kruskal(int n) : uf(n){}
    void addEdge(int u, int v, T c){
        es.emplace_back(u, v, c);
    }
    T build(){
        sort(begin(es), end(es));
        T res = 0;
        for(auto& e : es){
            if(!uf.same(e.from, e.to)){
                res += e.cost;
                uf.unite(e.from, e.to);
                e.used = true;
            }
        }
        return res;
    }
    Edge operator[](int i) const {
        return es[i];
    }
    vector<Edge> edgeSet() const {
        return es;
    }
};


signed main(){
    int N, M;
    while(cin >> N >> M, N+M){
        Kruskal<int> g(N);
        for(int i = 0;i < M;++i){
            int a, b, c;
            cin >> a >> b >> c;
            g.addEdge(a, b, c);
        }
        cout << g.build() << endl;
    }
    return 0;
}