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 <queue>
#include <vector>

using namespace std;

class Bridge
{
public:
	int from;
	int to;
	int cost;

	Bridge() : from(0), to(0), cost(0) {}
	Bridge(const Bridge& b) : from(b.from), to(b.to), cost(b.cost) {}

	bool operator > (const Bridge& b) const
	{
		return cost > b.cost;
	}

	bool operator < (const Bridge& b) const
	{
		return cost < b.cost;
	}
};



int nCity, nBridge;

Bridge bridge[100];
bool city[100];

int main()
{
	while( 1 )
	{
		//load data
		cin >> nCity >> nBridge;
		if(nCity == 0 && nBridge == 0)
		{
			break;
		}

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

		for(int i=0; i<nCity; i++)
		{
			city[i] = false;
		}

		//set initial node to queue
		priority_queue<Bridge, vector<Bridge>, greater<Bridge> > que;
		for(int i=0; i<nBridge; i++)
		{
			if(bridge[i].from == 0 || bridge[i].to == 0)
			{
				que.push(bridge[i]);
			}
		}

		city[0] = true;

		//iteration
		int totalCost = 0;
		while(!que.empty())
		{
			//end check
			bool isEnd = true;
			for(int i=0; i<nCity; i++)
			{
				if(!city[i])
				{
					isEnd = false;
					break;
				}
			}

			if(isEnd)
			{
				break;
			}

			//check highest priority node
			Bridge current = que.top();
			que.pop();

			totalCost += current.cost;

			int next = 0;
			if(!city[current.to])
			{
				city[current.to] = true;
				next = current.to;
			}
		
			if(!city[current.from])
			{
				city[current.from] = true;
				next = current.from;
			}

			for(int i=0; i<nBridge; i++)
			{
				if(bridge[i].to == next || bridge[i].from == next)
				{
					if(!city[bridge[i].to] || !city[bridge[i].from])
					{
						que.push(bridge[i]);
					}
				}
			}
		}

		printf("%d\n", totalCost);
	}
}

C++: #include<iostream>
#include<algorithm>

const int MAX_N = 100, MAX_M = 100, INF = 1 << 24;
int n, m;
int cost[MAX_N][MAX_N], mincost[MAX_N], used[MAX_N];

int prim(){
	std::fill(mincost, mincost+MAX_N, INF);
	std::fill(used, used+MAX_N, 0);

	mincost[0] = 0;
	int res = 0;
	while(true){
		int v = -1;
		for(int i=0;i<n;i++){
			if(!used[i] && (v == -1 || mincost[i] < mincost[v])){
				v = i;
			}
		}

		if(v == -1){
			break;
		}
		used[v] = 1;
		res += mincost[v];

		for(int i=0;i<n;i++){
			mincost[i] = std::min(mincost[i], cost[v][i]);
		}
	}

	return res;
}

int main(){
	while(std::cin >> n >> m, n){
		for(int i=0;i<MAX_N;i++){
			std::fill(cost[i], cost[i]+MAX_N, INF);
		}
		for(int i=0;i<m;i++){
			int a, b, c;
			std::cin >> a >> b >> c;
			cost[a][b] = c;
			cost[b][a] = c;
		}
		std::cout << prim() << std::endl;
	}
}

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

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