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 <iostream>
#include <vector>
#include <algorithm>
using namespace std;

struct edge{ int a,b,cost; };

int parent[100],height[100];

bool comp(const edge& e1,const edge& e2){
	return e1.cost < e2.cost;
}

int find(int x){
	if(parent[x] == x) return x;
	else return parent[x] = find(parent[x]);
}

void unite(int x,int y){
	x = find(x);
	y = find(y);
	if(x == y) return;
	if(height[x] < height[y]){
		parent[x] = y;
	}else {
		parent[y] = x;
		if(height[x] == height[y]) height[x]++;
	}
}

bool same(int x,int y){
	return find(x) == find(y);
}

int main(){
	int n,res = 0;
	cin >> n;
	vector<edge> es;
	for(int i = 0;i < n;i++) parent[i] = i;
	for(int i = 0;i < n;i++){
		for(int j = 0;j < n;j++){
			int t;
			cin >> t;
			if(t != -1) es.push_back({i,j,t});
		}
	}
	sort(es.begin(),es.end(),comp);
	for(int i = 0;i < es.size();i++){
		edge e = es[i];
		if(!same(e.a,e.b)){
			unite(e.a,e.b);
			res += e.cost;
		}
	}
	cout << res << endl;
	return 0;
}

C++: //最小生成树Prim算法
#include <iostream>

using namespace std;

const int N = 100;
const int INFTY = 1 << 14; //赋值无穷大

int n; //图的规模

short  Graph[N][N];

int *p; //p[i]记录着它们之间最小权值那个路径上，i的父节点
int *d;//d[i]标记着从i的父节点到i所需的最小权值
char *color; //标记节点是否访问状态


void prim() { //普莱姆算法
    for (int i=0;i<n;i++) {
    	d[i] = INFTY;
    	color[i] = 'W';
	}
	//普莱姆算法选取任意点作为开始点，这里我们选取第一个点 
	p[0] = INFTY;
	d[0] = 0;
	
	while (1) {
		
		//每次从剩余点中选取权值最小的点 
		int mincost = INFTY;
		int u;
		for (int i=0;i<n;i++) {
			if (color[i] != 'B' && mincost > d[i]) {
				mincost = d[i];
				u = i;
			}
		}
		
		if (mincost == INFTY) { //说明所有节点已经访问完毕 
			break;
		}
		
		color[u] = 'B'; //标记节点已经访问结束 
		
		for (int v=0;v<n;v++) {
			if (color[v] != 'B' && Graph[u][v] != INFTY) {
				if (d[v] > Graph[u][v]) {
					d[v] = Graph[u][v];
					p[v] = u;
					color[v] = 'G';
				}
			}
		}
	}
	
}

int main() {
	cin >> n;
	p = new int[n];
	d = new int[n];
	color = new char[n];

	for (int i=0; i<n; i++) {
		for (int j = 0; j<n; j++) {
			cin >> Graph[i][j];
			if (Graph[i][j] == -1) {
				Graph[i][j] = INFTY;
			}
		}
	}
	
	prim();
	int sum = 0;
	for (int i=0; i<n; i++) {
		if (p[i] != INFTY) {
			sum += Graph[i][p[i]];
		}
	}
	cout << sum << endl;
	delete[] p;
	delete[] d;
	delete[] color;
	return 0;
}

C++: //専用ライブラリ
#include <iostream>
#include <iomanip>
#include <istream>
#include <ostream>
#include <sstream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <queue>
#include <deque>
#include <list>
#include <stack>
#include <map>
#include <set>
#include <utility>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <ctime>
#include <cctype>
#include <cstdlib>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll>P;
#define INF 10e16
#define MOD 1000000007
#define rep(i, a, n) for (ll i = a; i < (ll)(n); i++)
#define fi first
#define se second
#define mmax(x,y)(x>y?x:y)
#define mmin(x,y)(x<y?x:y)
#define PI acos(-1.0)
long long GCD(long long a, long long b) { return b ? GCD(b, a%b) : a; }
long long LCM(long long a, long long b)  {return a/GCD(a,b)*b;}
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
int cmp(P a,P b){
        if(a.fi!=b.fi)
        return a.fi>b.fi;
        else
        return a.se<b.se;
}
//---------------------------------------------------------------------------
#define INFTY 2001
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define N 100

// 最小全域木を構成し、重みの総和を返す関数
int prim(int n, int A[N][N]) {
  int i, vertex, min_cost, sum_weight, cost[N], color[N];
  // 初期化
  for (i = 0; i < n; i++) {
    cost[i] = INFTY;
    color[i] = WHITE;
  }
  cost[0] = 0;
  color[0] = GRAY;
  sum_weight = 0;
  
  while (1) {
    // Tに隣接する頂点の中で最小のコストを持つものを選ぶ
    vertex = -1;
    min_cost = INFTY;
    for (i = 0; i < n; i++) {
      if (color[i] == GRAY && cost[i] < min_cost) {
        min_cost = cost[i];
        vertex = i;
      }
    }
    // T = V ならば終了
    if (vertex == -1) break;

    color[vertex] = BLACK;  // vertexをTに加える
    sum_weight += cost[vertex];

    // vertexに隣接し、Tに属していない頂点のコストを更新
    for (i = 0; i < n; i++) {
      if (color[i] != BLACK && A[vertex][i] < INFTY) {
        color[i] = GRAY;
        if (cost[i] > A[vertex][i]) cost[i] = A[vertex][i];
      }
    }
  }

  return sum_weight;
}

/*
// 最小全域木の辺の重みの和を計算する関数
int sum_weight(int n, int parent[], int A[N][N]) {
  int sum = 0;
  
  for (int i = 1; i < n; i++) sum += A[i][parent[i]];
  
  return sum;
}*/

//---------------------------------------------------------------------------
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    //-------------------------------
    int i, j, n, w, A[N][N];
    cin >> n;
    // 隣接行列が与えられる
    for (i = 0; i < n; i++) {
      for (j = 0; j < n; j++) {
        cin >> w;
        if (w == -1) A[i][j] = INFTY;
        else A[i][j] = w;
      }
    }

    cout << prim(n, A) << endl;
    //-------------------------------
    return 0;
}
//---------------------------------------------------------------------------