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 <set>
#include <algorithm>
#include <vector>

using namespace std;

int n, m;
vector< set< pair<int, int> > > cost(100,set< pair<int,int> >());

int prim()
{
	int res=0;
	set<int> v;
	v.insert(0);
	while(v.size()<n)
	{
		pair<int, int> mini(100000007, -1);
		for(set<int>::iterator it=v.begin();it!=v.end();it++)
		{
			for(set<  pair<int, int> >::iterator it2=cost[*it].begin();it2!=cost[*it].end();it2++)
				if(v.find((*it2).second)==v.end())
				{
					if(mini.first>(*it2).first)
						mini=(*it2);
					break;
				}
		}
		v.insert(mini.second);
		res+=mini.first;
	}
	return res;
}

int main()
{
	while(1)
	{
		cin >> n >> m;
		if(n==0&&m==0) break;
		for(int i=0;i<m;i++)
		{
			int a, b, c;
			cin >> a >> b >> c;
			cost[a].insert(pair<int, int>(c, b));
			cost[b].insert(pair<int, int>(c, a));
		}
		cout << prim() << endl;
		for(int i=0;i<m;i++)
			cost[i].clear();
	}
	return 0;
}

C++: /*
 * 隣接リスト表現のグラフのプリム法 (優先度付きキューを使用)
 * 計算量は O(|E| log |V|)
 *
 */
#include <iostream>
#include <vector>
#include <map>
#include <queue>
#include <algorithm>
using namespace std;

const int MAX_V = 10000;
const int INF = 1e+8;
// first : コスト, second : 頂点番号
typedef pair<int,int> P;

struct edge{
	int to, cost;
	edge(int v, int cost_){
		to = v;
		cost = cost_;
	}
};

// 頂点数
int V;
// G[u][i] = ノード u に接続している i 番目の edge が返ってくる
vector<edge> G[MAX_V];
// 頂点の集合 X からの辺の最小コスト
int mincost[MAX_V];
// used[i] := 頂点 i が集合に含まれているか
bool used[MAX_V];

// 初期化
void init(int n){
	V = n;
	for(int i = 0 ; i < MAX_V ; i++ ){
		G[i].clear();
	}
}

// 最小全域木のコストの総和を返す (プリム法)
int prim(){
	// greater<P> を指定することで first が小さい順に取り出せる
	priority_queue<P, vector<P>, greater<P> > q;
	// 初期化
	fill( mincost , mincost+V , INF );
	fill( used , used+V , false );
	mincost[0] = 0;
	int res = 0;
	q.push( P(0,0) );
	
	while( !q.empty() ){
		P p = q.top(); q.pop();
		int v = p.second;
		
		if( mincost[v] < p.first ) continue;
		used[v] = true;
		res += mincost[v];
		
		for(int i=0 ; i < G[v].size() ; i++ ){
			edge e = G[v][i];
			if( !used[e.to] && mincost[e.to] > e.cost ){
				mincost[e.to] = e.cost;
				q.push( P(e.cost,e.to) );
			}
		}
	}
	return res;
}

// 重み cost の辺 (u,v) の追加
void add_edge(int u, int v, int cost){
	edge e( v , cost );
	G[u].push_back( e );
	// 有向グラフなら以下の処理は不要
	e.to = u;
	G[v].push_back( e );
}

int main(){
	int n,m;
	while( cin >> n >> m , n || m ){
		// 初期化
		init( n );
		for(int i = 0 ; i < m ; i++ ){
			int u, v, c ;
			cin >> u >> v >> c;
			add_edge( u , v , c );
		}
		cout << prim() << endl;
	}
}

C++: #include <iostream>
#include <queue>
#include <vector>
#include <functional>

using namespace std;

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

	Bridge() : from(0), to(0), cost(0) {}

	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[101];
bool city[101];

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

		for(int i=0; i<nBridge; i++)
		{
			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( 1 )
		{
			//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 && !city[bridge[i].from]) || 
				   (bridge[i].from == next && !city[bridge[i].to]))
				{
					que.push(bridge[i]);
				}
			}
		}

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

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

using namespace std;

int n, m;
vector< set< pair<int, int> > > cost(100,set< pair<int,int> >());

int prim()
{
	int res=0;
	set<int> v;
	v.insert(0);
	while(v.size()<n)
	{
		pair<int, int> mini(100000007, -1);
		for(set<int>::iterator it=v.begin();it!=v.end();it++)
		{
			for(set<  pair<int, int> >::iterator it2=cost[*it].begin();it2!=cost[*it].end();it2++)
				if(v.find((*it2).second)==v.end())
				{
					if(mini.first>(*it2).first)
						mini=(*it2);
					break;
				}
		}
		v.insert(mini.second);
		res+=mini.first;
	}
	return res;
}

int main()
{
	while(1)
	{
		cin >> n >> m;
		if(n==0&&m==0) break;
		for(int i=0;i<m;i++)
		{
			int a, b, c;
			cin >> a >> b >> c;
			cost[a].insert(pair<int, int>(c, b));
			cost[b].insert(pair<int, int>(c, a));
		}
		cout << prim() << endl;
		for(int i=0;i<m;i++)
			cost[i].clear();
	}
	return 0;
}