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<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pll;
typedef pair<int,pll> P;
struct unionfind{
  int par[110]; // 親ノード  必要に応じて要素数を変えよう
  int rank[110]; // ランク　必要に応じて要素数を変えよう
  unionfind(int n){
    init(n);
  }
  void init(int n){
    for(int i=0;i<=n;i++){
      par[i]=i;
      rank[i]=1;
    }
  }
  int root(int x) {
    if (par[x] == x) {
      return x;
    }
    else {
      return par[x] = root(par[x]);
    }
  }
  int size(int x){
    return rank[root(x)];
  }
  bool same(int x,int y) {
    return root(x) == root(y);
  }
  void unite(int x,int y) {
    x=root(x);
    y=root(y);
    if(x==y){
      return;
    }
    if(rank[x]<rank[y]){
      swap(x,y);
    }
    rank[x]=rank[x]+rank[y];
    par[y]=x;
  }
};
int main(){
  while(1){
    int n,m,i;
    cin >> n >> m;
    if(n==0 && m==0){
      return 0;
    }
    unionfind tree(n);
    vector<P> g;
    for(i=0;i<m;i++){
      int a,b,c;
      cin >> a >> b >> c;
      g.push_back(make_pair(c,pll(a,b)));
    }
    sort(g.begin(),g.end());
    int ans=0;
    for(i=0;i<m;i++){
      if(!tree.same(g[i].second.first,g[i].second.second)){
        tree.unite(g[i].second.first,g[i].second.second);
        ans+=g[i].first;
      }
    }
    cout << ans << endl;
  }
}

C++: #include <iostream>
#include <vector>
#include <climits>

int main(){
  int a[2];
  while(std::cin >> a[0] >> a[1]){
    int i,j;
    int city[a[0]][a[0]];
    int Tcity[a[0]];
    int cost = 0;
    for(i=0; i<a[0]; i++){
      Tcity[i] = 0;
      for(j=0; j<a[0]; j++){
        city[i][j] = INT_MAX;
      }
    }
    std::vector<std::vector<int> > v;
    for(i=0; i<a[1]; i++){
      std::vector<int> w;
      int s,g,c;
      std::cin >> s >> g >>c;
      city[s][g] = c;
      w.push_back(s);
      w.push_back(g);
      v.push_back(w);
    }
    Tcity[0] = 1;
    while(1){
      int min = INT_MAX;
      int min_s,min_g;
      for(i=0; i<a[0]; i++){
        if(Tcity[i] == 1){
          for(j=0; j<a[0]; j++){
            if(city[i][j] < min){
              min = city[i][j];
              min_s = i;
              min_g = j;
            }
          }
        }
      }
      Tcity[min_s] = 1;
      Tcity[min_g] = 1;
      cost += min;
      int loop = 1;
      for(j=0; j<a[0]; j++){
        if(Tcity[j] == 0) loop = 0;
      }
      if(loop){
        std::cout << cost << std::endl;
        break;
      }
    }
  }
  return 0;
}

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

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

vector<int> ans;
vector<vector<int>> cost(100,vector<int>(100,0));

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_;
}

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;
}