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++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;

int main() {
  int n;
  cin >> n;

  int G[n][n];
  int visited[n];
  int d[n];
  int p[n];
  REP(y, n) {
    REP(x, n) {
      int cost;
      cin >> cost;

      if (cost == -1) {
        G[y][x] = 1 << 15;
      } else {
        G[y][x] = cost;
      }
    }
    visited[y] = 0;
    d[y] = 1 << 15;
    p[y] = -1;
  }

  d[0] = 0;

  REP(_, n) {
    int mincost = 1 << 15;
    int minv;
    REP(v, n) {
      if (!visited[v] && d[v] < mincost) {
        minv = v;
      }
    }
    visited[minv] = 1;
    REP(to, n) {
      if (G[minv][to] < (1 << 15) && G[minv][to] < d[to]) {
        d[to] = G[minv][to];
        p[to] = minv;
      }
    }
  }

  ll sum = 0;
  REP(i, n) {
    if (p[i] != -1) {
      sum += G[i][p[i]];
    }
  }

  cout << sum << endl;
  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 n,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]!=balck&&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;
}

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

#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() {
  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;
}

C++: #include <iostream>
#include <algorithm>

using namespace std;

#define MAX_V 100
#define MAX_E 5050

int par[MAX_V],rank[MAX_V];
int V,E;

struct edge{ int u,v,cost; };
edge es[MAX_E];

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

void init(int n){
  for(int i = 0 ; i < n ; i++){
    par[i] = i;
    rank[i] = 0;
  }
}

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

void unite(int x,int y){
  x = find(x);
  y = find(y);

  if(x == y){
    return;
  }

  if(rank[x] < rank[y]){
    par[x] = y;
  }else{
    par[y] = x;
    if(rank[x] == rank[y]){
      rank[x]++;
    } 
  }
}

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

int kruskal(){
  sort(es, es + E, comp);

  init(V);
  int res = 0;

  for(int i = 0 ; i < E ; i++){
    edge e = es[i];

    if(!same(e.u,e.v)){
      unite(e.u,e.v);
      res += e.cost;
    }
  }
  return res;
}

int main(){
  int c;

  cin >> V;
  for(int i = 0 ; i < V ; i++){
    for(int j = 0 ; j < V ; j++){
      cin >> c;

      if(c == -1){
	continue;
      }

      edge e = {i,j,c};
      es[E++] = e;
    }
  }

  cout << kruskal() << endl; 

  return 0;
}