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 <bits/stdc++.h>

#define REP(i, n) for(int i = 0; i < n; i++)
using namespace std;

int P[10010];

void init(int N)
{
    for (int i = 0; i < N; i++) P[i] = i;
}

int root(int a)
{
    if (P[a] == a)  return a;
    return (P[a] = root(P[a]));
}

bool is_same_set(int a, int b)
{
    return root(a) == root(b);
}

void unite(int a, int b)
{
    P[root(a)] = root(b);
}

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

    vector<tuple<int, int, int>> pr;
    int a;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> a;
            if (a != -1 && i <= j) {
                pr.push_back(make_tuple(a, i, j));
            }
        }
    }

    sort(pr.begin(), pr.end());
    init(n);
    int cost = 0;

    for (int i = 0; i < pr.size(); i++) {
        int& a = get<1>(pr[i]);
        int& b = get<2>(pr[i]);

        if (!is_same_set(a, b)) {
            unite(a, b);
            cost += get<0>(pr[i]);
        }
    }
    cout << cost << endl;
}

C++: #include <iostream>

using namespace std;
static const int MAX = 100;
static const int INF = (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] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[0] = 0;

    while (true) {
        minv = INF;
        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] != INF) {
                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 ? INF : e;
        }
    }

    cout << prim() << endl;

    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#define MAX 105
#define INF 1000000
using namespace std;

int n;
int M[MAX][MAX];
int d[MAX];
int p[MAX];
int color[MAX];//0 表示未进入 -1 表示在之中 1 表示已出去

int prim() {
	int u,min,i,j;
	d[0]=0;
	p[0]=-1;
	while(1) {
		min=INF;
		u=-1;
		for(i=0; i<n; i++) {
			if(min>d[i] && color[i]!=1) {
				u=i;
				min=d[i];
			}
		}
		if(u==-1) break;
		color[u]=1;
		for(j=0; j<n; j++) {
			if(color[j]!=1 && M[u][j]!=INF) {
				if(d[j]>M[u][j]) {
					d[j]=M[u][j];
					color[j]=-1;
					p[j]=u;
				}
			}
		}
	}
	int sum=0;
	for(i=0; i<n; i++) {
		if(p[i] != -1) sum+=M[i][p[i]];
	}
	return sum;
}

int main() {
	int i,j,a;
	memset(color,0,sizeof(color));
	memset(d,INF,sizeof(d));
	memset(p,-1,sizeof(p));
	scanf("%d",&n);
	for(i=0; i<n; i++) {
		for(j=0; j<n; j++) {
			scanf("%d",&a);
			if(a==-1) a=INF;
			M[i][j]=a;
		}
	}
	cout<<prim();
	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;
}