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 <vector>
using namespace std;

struct Edge { int from, to, cost; };

int main() {
	int n, m, a, b, cost;
	while (cin >> n >> m, n) {
		vector<Edge> G;
		for (int i=0; i<m; ++i) {
			cin >> a >> b >> cost;
			G.push_back((Edge){ a, b, cost });
			G.push_back((Edge){ b, a, cost });
		}
		int ret = 0;
		bool used[100] = {};
		used[0] = true;
		while (1) {
			int k, mn = 1e5;
			for (int i=0; i<(int)G.size(); ++i) {
				if (used[G[i].from] && ! used[G[i].to] && G[i].cost < mn) {
					mn = G[i].cost;
					k = i;
				}
			}
			if (mn == 1e5) break;
			used[G[k].to] = true;
			ret += G[k].cost;
		}
		cout << ret << endl;
	}
	return 0;
}

C++: #include <iostream>
using namespace std;
const int INF = 1000000;

int main(){
	int n,m;
	while(cin >> n >> m){
		if(!n && !m)
			break;
		int bridge[101][101];
		int pre_vertex[101][101];
		int a,b,cost;
		for(int i=0;i<101;i++){
			for(int j=0;j<101;j++){
				if(i==j)
					bridge[i][j] = 0;
				else
					bridge[i][j] = INF;
				pre_vertex[i][j] = i;
			}
		}
		for(int i=0;i<m;i++){
			cin >> a >> b >> cost;
			if(bridge[a][b] > cost){
				bridge[a][b] = cost;
				bridge[b][a] = cost;
			}
		}
		for(int k=0;k<n;k++){
			for(int i=0;i<n;i++){
				for(int j=0;j<n;j++){
					int dis = bridge[i][k]+bridge[k][j];
					if(dis < bridge[i][j]){
						bridge[i][j] = dis;
						pre_vertex[i][j] = pre_vertex[k][j];
					}	
				}
			}
		}
		int min = INF;
		for(int i=0;i<n;i++){
			int sum = 0;
			for(int j=0;j<n;j++){
				sum += bridge[i][j] - bridge[i][pre_vertex[i][j]];
			}
			if(sum < min)
				min = sum;
		}
		cout << min << endl;
	}
	return 0;
}

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

class Graph {
private:
  const static int INF = 1000000; 
  std::vector<std::vector<int> > edge_;
  unsigned int size_;
public:
  Graph(unsigned int size);
  Graph& connect(int from, int to, int weight);
  std::vector<int> neighbours(int node) const;
  unsigned int size() const;
};

const int Graph::INF;

Graph::Graph(unsigned int size) {
  size_ = size;
  edge_ = std::vector<std::vector<int> > (size_, std::vector<int>(size_, INF));
}

Graph& Graph::connect(int from, int to, int weight = 1) {
  edge_[from][to] = weight;
  return *this;
}

std::vector<int> Graph::neighbours(int node) const {
  std::vector<int> neighbours;
  for (int i = 0; i < static_cast<int>(size_); ++i)
    if (edge_[node][i] < INF) neighbours.push_back(i);

  return neighbours;
}

unsigned int Graph::size() const {
  return size_;
}


Graph creat_graph(int n, int m);
int search_prim(Graph prim, int n);

vector<int> ans;
vector<vector<int>> cost;

int main(){
  int n,m;
 
  
  while(cin >> n >> m, n){     
    Graph prim = creat_graph(n,m);   /*creat graph*/
    ans.push_back(search_prim(prim,n));   /*make answer*/
  }
  
  for(int i: ans){
    cout << i << endl;
  }
  return 0;
}


 Graph creat_graph(int n,int m){
    Graph prim(n);
    int a,b,cost_t;

    for(int i=0; i<m; i++){
      cin >> a >> b >> cost_t;
      prim.connect(a,b);
      cost[a][b] = cost_t;
      cost[a][b] = cost_t;
    }
    return prim;
  }
    
int search_prim(Graph prim, int n){
  int current,cost_sum;
  typedef pair<int, int> PII;
  vector<bool> frag(n,false);
  priority_queue < PII, vector < pair <int, int> >, greater < pair <int, int> > > que;
  /*cost,next_node*/
  
  cost_sum = 0;
  current = 0;
  frag[0] = true;
  for(int k=0; k<n-1; ++k){
     vector<int> near = prim.neighbours(current);

     for(int j:near){
       que.push(PII(cost[current][j],j));
     }

     while(1){
       if(frag[que.top().second] == false){
	 cost_sum += que.top().first;
	 frag[que.top().second] = true;
	 current = que.top().second;
	 break;
	 }
     }
     que.pop();
  }
  return cost_sum;
}

C++: #include<iostream>
#include<queue>
#include<vector>
#include<functional>
using namespace std;
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define MAX_N 1000
#define INF 1000000000
int dist[MAX_N], color[MAX_N]; vector<pair<int, int> >X[MAX_N];
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > >Q;
long long prim(int V) {
	for (int i = 0; i < V; i++) { dist[i] = INF; color[i] = WHITE; }
	dist[0] = 0; color[0] = GRAY; Q.push(make_pair(0, 0));
	while (!Q.empty()) {
		pair<int, int>pa = Q.top(); Q.pop();
		int a1 = pa.first, a2 = pa.second; color[a2] = BLACK;
		for (int i = 0; i < X[a2].size(); i++) {
			int to = X[a2][i].first, leng = X[a2][i].second;
			if (dist[to] > leng && color[to] < BLACK) {
				dist[to] = leng; Q.push(make_pair(dist[to], to));
			}
		}
	}
	long long sum = 0; for (int i = 0; i < V; i++) { sum += dist[i]; }//0-indexed
	return sum;
}
int main() {
	int N, M, a, b, c;
	while (true) {
		for (int i = 0; i < MAX_N; i++) { X[i].clear(); }
		cin >> N >> M; if (N == 0 && M == 0) { break; }
		for (int i = 0; i < M; i++) {
			cin >> a >> b >> c; X[a].push_back(make_pair(b, c));
			X[b].push_back(make_pair(a, c));
		}
		cout << prim(N) << endl;
	}
	return 0;
}