Go: package main

import (
	"sort"
	"bufio"
	"os"
	"fmt"
	"strconv"
)

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

C++: #include <bits/stdc++.h>
#define r(i,a,n) for(int i=a;i<n;i++)
using namespace std;
int main(){
	int n,p;
	while(cin>>n>>p,n){
		int q,a[10000][1261],ch[10000][1261],b,c,d,e;
		r(i,0,p)r(j,0,1261)ch[i][j]=a[i][j]=0;
		cin>>q;
		r(i,0,q){
			cin>>b>>c>>d>>e;
			if(e==1){a[d-1][b]++;ch[d-1][b]=c;}
			else{
				for(int j=b-1;j>=0;j--){
					if(ch[d-1][j]==c)break;
					a[d-1][j]++;
				}
			}
		}
		cin>>q;
		while(q--){
			int s=0;
			cin>>b>>c>>d;
			r(i,b,c)if(a[d-1][i])s++;
			cout<<s<<endl;
		}
	}return 0;
}

C++: #include <iostream>
#include <queue>
#include <vector>
#include <utility>
using namespace std;
typedef pair<int,int> Info;
int main(){
        int N;
        cin >> N;
        vector <vector<int> > adjancey(N,vector<int>(N));
        priority_queue<Info, vector<Info>,greater<Info> > descending;
        for(int i=0 ; i<N ; i++ )
                for(int j=0 ; j<N ; j++ )
                        cin >> adjancey[i][j];
        Info wn;
        int now=0,counter=0;
        vector <bool> past(N,false);
        while(true){
                past[now]=true;
                for(int i=0 ; i<N ; i++ ){
                        if(past[i])
                                continue;
                        if(adjancey[now][i]==-1)
                                continue;
                        wn.first=adjancey[now][i];
                        wn.second=i;
                        descending.push(wn);
                }
                wn=descending.top();descending.pop();
                now=wn.second;
                if(past[now])break;
                counter+=wn.first;
        }
        cout << counter << endl;
        return 0;
}

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

#define INF 2000000000

int x[10000][10000];
int MIN[10000];
int p[10000];

int prim(){
    int v,MINX;
    int col[10000];
    for(int i=0;i<n;i++){
        MIN[i]=INF;
        p[i]=-1;
        col[i]=0;
    }
    MIN[0]=0;
    while(true){
        MINX=INF;
        v=-1;
        for(int i=0;i<n;i++){
            if(MINX > MIN[i] && col != 2){
                u=i;
                MINX = MIN[i];
            }
        }
        if(u==-1){
            break;
        }
        color[u]=black;
        for(int k=0;k<n;k++){
            if(color != 0 && x[u][k]!=-1 && MIN[k]>x[u][k]){
                MIN[k]=x[u][k];
                col[k]=1;
            }
        }
    }
    int sum=0;
    for(int i=0;i<n;i++){
        sum += x[i][MIN[i]];
    }
    return sum;
}

int main() {
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
    cout<<prim()<<endl;
	return 0;
}

C++: #include <stdio.h>
int main(){
    int n, i, j, t, a[100][100];
    int u, min, d[100], p[100], v[100];
    scanf("%d", &n);
    for(i = 0; i < n; i++) for(j = 0; j < n; j++) {
        scanf("%d", &t);
        a[i][j] = (t==-1)?1000000000:t;
    }
    for(i = 0; i < n; i++) {
        d[i] = 1000000000;
        p[i] = -1;
        v[i] = 0;
    }
    d[0] = 0;
    while(1) {
        min = 1000000000;
        u = -1;
        for(i = 0; i < n; i++) {
            if(min > d[i] && v[i] != 2) {
                u = i;
                min = d[i];
            }
        }
        if(u == -1) break;
        v[u] = 2;
        for(j = 0; j < n; j++) {
            if(v[j] != 2 && a[i][j] != 1000000000){
                if(d[j] > a[u][j]) {
                    d[j] = a[u][j];
                    p[j] = u;
                    v[j] = 1;
                }
            }
        }
        t = 0;
        for(i = 0; i < n; i++) {
            if(p[i] != -1) t+=a[i][p[i]];
        }
    }
    printf("%d\n", t);
    return 0;
}

C++: #include<iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, M[MAX][MAX];

int prim() {
	int u, minv;
	int d[MAX], p[MAX], color[MAX];
	
	for(int i = 0; i < n; i++) {
		d[i] = INFTY;
		p[i] = -1;
		color[i] = WHITE;
	}
	
	d[0] = 0;
	
	while(1) {
		minv = INFTY;
		u = -1;
		for(int i = 0; i < n; i++) {
			if(minv > d[i] && color[i] != BLACK) {
				u = i;
				minv = d[i];
			}
		}
	   if(u == -1) break;
	   color[u] = BLACK;
	   for(int v = 0; v < n; v++) {
           if(color[v] != BLACK && M[u][v] != INFTY){
		   	  if(d[v] > M[u][v]) {
	   		      d[v] = M[u][v];
   		          p[v] = u;
           	   	  color[v] = GRAY;
   	           }
           }
   	   }	
	}
	int sum = 0; 
	for(int i = 0; i < n; i++) {
		if(p[i] != -1) sum += M[i][p[i]];
	}
	return sum;
} 

int main() {
	cin >> n;
	
	for(int i = 0; i < n; i++) {
		for(int j = 0; j < n; j++){
			int e;
			cin >> e;
			M[i][j] = (e == -1) ? INFTY :e;
		}
	}
	
	cout << prim() << endl;
	
	return 0;
}