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++: n = int(raw_input())
A = [0]
i = 0
long = 0
NY = range(1, n)
a = [[0 for i in xrange(n)] for j in xrange(n)]
while i <=n:
    a[i] = map(int,raw_input().split())
    i = i+1
while NY != []:
    amin = 2001
    for i in A:
        for j in NY:
            if 0 <= a[i][j] < amin:
                amin = a[i][j]
                addA = j
    A.append(addA)
    NY.remove(addA)
    long =long + amin
print long

C++: #include <bits/stdc++.h>
using namespace std;

int n;
vector< vector<int> > a;

int Prim() {
  vector<int> color(n);
  vector<int> d(n, 1000000000);
  vector<int> p(n);
  d[0] = 0, p[0] = -1;

  while (true) {
    int min_cost = 1000000000, u;
    for (int i = 0; i < n; i++) if (color[i] != 2 && d[i] < min_cost) min_cost = d[i], u = i;
    if (min_cost == 1000000000) break;
    color[u] = 2;
    for (int v = 0; v < n; v++)
      if (color[v] != 2 && a[u][v] != -1)
        if (a[u][v] < d[v]) d[v] = a[u][v], p[v] = u, color[v] = 1;
  }

  int ans = 0;
  for (int i = 0; i < n; i++) if(p[i]!=-1 )ans += a[i][p[i]];

  return ans;
}

int main() {
  cin >> n;
  a.resize(n, vector<int>(n));
  for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) cin >> a[i][j];
  cout << Prim() << endl;
}

C++: #include <iostream>
using namespace std;
const int maxx=110;
const int infinity=(1<<30);

int A[maxx][maxx];
bool flag[maxx];	//用flag来标记这个节点是不是在MST中，true是在T里，false是在V-T里；

int main (){
		int n;
		cin>>n;
		for(int i =1;i<=n;i++){
			for(int j=1;j<=n;j++){
				int e;cin>>e;
				A[i][j]=(e==-1)?infinity:e;
			}
		}

		for(int i=0;i<maxx;i++) flag[i]=false;
		int sum=0,minv,minj;
		flag[1]=true;
		while(1){
			minv=infinity;
			minj=-1;
			for(int i=1;i<=n;i++){
				if(flag[i]==true){
					for(int j=1;j<=n;j++){
						if(A[i][j]!=-1 && A[i][j]<minv && flag[j]==false) {
							minv=A[i][j];
							minj=j;
						} 
					}
				}
			}
//			cout<<minj<<endl;
			if(minv==infinity || minj==-1) break;
			flag[minj]=true;
			sum+=minv;
		}
		
		cout<<sum<<endl;
		return 0;
		
}

C++: #include <bits/stdc++.h>
using namespace std;

const int INFY = numeric_limits<int>().max();
int n;
typedef vector<vector<int>> GM;

int prim(GM &G) {
    vector<bool> inmst(n, false);
    vector<int> d(n, INFY);
    vector<int> p(n, -1);

    d[0] = 0;
    while(true) {
        int u = -1, minv = INFY;
        for (int i = 0; i < n; ++i) {
            if(!inmst[i] && d[i] < minv) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1) break;
        inmst[u] = true;
        for (int i = 0; i < n; ++i) {
            if (!inmst[i] && G[u][i] != INFY) {
                if (G[u][i] < d[i]) {
                    d[i] = G[u][i];
                    p[i] = u;
                }
            }
        }
    }
    int sum = 0;
    for (int i = 0; i < n; ++i) {
        if(p[i] != -1) sum += G[i][p[i]];
    }
    return sum;
}

int main() {
    cin >> n;
    GM G(n, vector<int>(n));
    for(int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int c;
            cin >> c;
            G[i][j] = c == -1 ? INFY : c;
        }
    }
    cout << prim(G) << endl;
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int NOT_VISIT = 0;
static const int VISITING = 1;
static const int VISITED = 2;
int n;
int M[MAX][MAX];
int prim()
{
    int minv, u;
    int isVisited[MAX], d[MAX], p[MAX];
    for (int i = 0; i < n; i++) {
	isVisited[i] = NOT_VISIT;
	d[i] = INFTY;
	p[i] = -1;
    }
    d[0] = 0;
    while (1) {
	minv = INFTY;
	u = -1;
	for (int i = 0; i < n; i++) {
	    if (minv > d[i] && isVisited[i] != VISITED) {
		u = i;
		minv = d[i];
	    }
	}
	if (u == -1) {
	    break;
	}

	isVisited[u] = VISITED;
	for (int j = 0; j < n; j++) {
	    if (isVisited[j] != VISITED && M[u][j] != INFTY) {
		if (d[j] > M[u][j]) {
		    d[j] = M[u][j];
		    p[j] = u;
		    isVisited[j] = VISITING;
		}
	    }
	}
    }
    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;
}