Go: package main

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

const (
	MAX_N      = 200
	MAX_WEIGHT = 2000
)

type Edge struct {
	start  int
	end    int
	weight int
}

type ShortestInfo struct {
	edges    []Edge
	shortest int
}

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

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

	shortestList := make([]ShortestInfo, n)
	for i := 1; i < n; i++ {
		shortestList[i] = ShortestInfo{edges: []Edge{}, shortest: MAX_N*MAX_WEIGHT + 1}
	}

	adjacentMatrix := make([][]int, n)
	for i := 0; i < n; i++ {
		adjacentMatrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			v, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjacentMatrix[i][j] = v
		}
	}

	mst([]int{1}, shortestList, adjacentMatrix)
	fmt.Println(calculateMinWeight(shortestList))
}

func calculateMinWeight(shortestList []ShortestInfo) int {
	visitedList := make([]bool, len(shortestList))
	visitedList[0] = true
	sumWeight := 0
	for !visitedAll(visitedList) {
		shortestInfo := shortestList[0]
		shortestList = shortestList[1:]
		edges := shortestInfo.edges
		for _, edge := range edges {
			if !visitedList[edge.end-1] {
				visitedList[edge.end-1] = true
				sumWeight += edge.weight
			}
		}
	}
	return sumWeight
}

func visitedAll(visitedList []bool) bool {
	for _, v := range visitedList {
		if !v {
			return false
		}
	}
	return true
}

func mst(nodeStack []int, shortestList []ShortestInfo, adjacentMatrix [][]int) {
	for len(nodeStack) > 0 {
		currentNode := nodeStack[0]
		nodeStack = nodeStack[1:]
		currentShortest := getShortest(currentNode, shortestList)
		adjacents := findAdjacents(currentNode, adjacentMatrix)
		for i := 0; i < len(adjacents); i++ {
			adj := adjacents[i]
			s := getShortest(adj.end, shortestList)
			if currentShortest.shortest+adj.weight < s.shortest || (currentShortest.shortest+adj.weight == s.shortest && len(currentShortest.edges)+1 > len(s.edges)) {
				setShortest(adj.end, adj, currentShortest, shortestList)
				nodeStack = append(nodeStack, adj.end)
			}
		}
	}
}

func getShortest(node int, shortestList []ShortestInfo) ShortestInfo {
	return shortestList[node-1]
}

func setShortest(node int, edge Edge, currentShortest ShortestInfo, shortestList []ShortestInfo) {
	newEdges := make([]Edge, len(currentShortest.edges)+1)
	for i := 0; i < len(newEdges)-1; i++ {
		newEdges[i] = currentShortest.edges[i]
	}
	newEdges[len(newEdges)-1] = edge
	shortestInfo := ShortestInfo{edges: newEdges, shortest: currentShortest.shortest + edge.weight}
	shortestList[node-1] = shortestInfo
}

func findAdjacents(currentNode int, adjacentMatrix [][]int) []Edge {
	adjacents := adjacentMatrix[currentNode-1]
	edges := []Edge{}
	for i, v := range adjacents {
		if v > 0 {
			edges = append(edges, Edge{start: currentNode, end: i + 1, weight: v})
		}
	}
	return edges
}

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

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
//#include "MyMath.h"
//#include "MyDisjointset.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <functional>
#include <stdio.h>
using namespace std;
typedef pair<int, int> P;
const int INF = 2000000000;
int main() {
	int n; cin >> n;
	int m[101][101];
	for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)
		cin >> m[i][j];
	int res = 0;
	int *d = new int[n];
	fill(d, d + n, INF); 
	d[0] = 0;
	bool *visit = new bool [n];
	fill(visit, visit + n, false);
	priority_queue <P, vector<P>, greater<P> > q;
	q.push(P(d[0], 0));
	while (!q.empty()) {
		int f = q.top().first, s = q.top().second;
		visit[s] = true;
		res += f;
		q.pop();
		for (int i = 0; i < n; i++) {
			if (!visit[i]) {
				if (m[s][i] != -1) {
					if (m[s][i] < d[i]) {
						d[i] = m[s][i];
						q.push(P(d[i], i));
					}
				}
				}
			}
		}
	cout << res << endl;
	delete[] d, visit;
	return 0;

C++: #include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef pair<int, int> P;

// Kruskal法
//   証明: http://drken1215.hatenablog.com/entry/20121223/1356230697

class UnionFind {
    vector<int> par;
    int n;
public:
    UnionFind(int sz) : par(sz, -1) {}
    int find(int x) {
        if (par[x] < 0) return x;
        return par[x] = find(par[x]);
    }
    bool unite(int x, int y) {
        x = find(x); y = find(y);
        if (x == y) return false;
        if (par[x] > par[y]) swap(x, y);
        par[x] += par[y];
        par[y] = x;
        return true;
    }
    bool same(int x, int y) { return find(x) == find(y); }
    int size(int x) { return -par[find(x)]; }
};

int kruskal(vector<vector<P>> &edge) {
    int n = edge.size();
    typedef pair<int, P> PP;
    vector<PP> weights;
    for (int i = 0; i < n; i++) {
        for (auto &e : edge[i]) weights.push_back({e.second, {i, e.first}});
    }
    sort(weights.begin(), weights.end());
    UnionFind uf(n);
    int ret = 0;
    for (auto &w : weights) {
        int from = w.second.first;
        int to = w.second.second;
        if (uf.unite(from, to)) ret += w.first;
    }
    return ret;
};


// verified
//   http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_2_A&lang=jp
void AOJ_GRL_2_A() {
    int V, E;
    cin >> V >> E;
    vector<vector<P>> edge(V);
    for (int i = 0; i < E; i++) {
        int s, t, w;
        cin >> s >> t >> w;
        edge[s].push_back({t, w});
    }
    cout << kruskal(edge) << endl;
}

// verified
//   http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A&lang=jp
void AOJ_ALDS1_12_A() {
    int n;
    cin >> n;
    vector<vector<P>> edge(n);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int w;
            cin >> w;
            if (w < 0) continue;
            if (j < i) continue;
            edge[i].push_back({j, w});
        }
    }
    cout << kruskal(edge) << endl;
}

int main() {
    // AOJ_GRL_2_A();
    AOJ_ALDS1_12_A();
    return 0;
}

C++: #include <iostream>
#define N 100
#define WHITE 0
#define BLACK 1
#define INF 10000

using namespace std;

int M[N][N],n,d[N];

void prim(){
  int color[n],p[n];
  for(int i=0;i<n;i++){
    color[i]=WHITE;
    d[i]=INF;
  }
  d[0]=0;
  p[0]=-1;
  while(1){
    int mincost=INF;
    int u;
    for(int i=0;i<n;i++){
      if(color[i]!=BLACK && d[i]<mincost){
        mincost=d[i];
        u=i;
      }
    }
    if(mincost==INF) break;
    //connect u to p[u]
    color[u]=BLACK;
    for(int v=0;v<n;v++){
      if(color[v]!=BLACK && M[u][v]!=-1){
        if(M[u][v]<d[v]){
          d[v]=M[u][v];
          p[v]=u;
        }
      }
    }
  }
}

int main(){
  cin >> n;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++) cin >> M[i][j];
  }
  prim();
  int sum=0;
  for(int i=0;i<n;i++) sum+=d[i];
  cout << sum << endl;
}