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>
const int MAX_N = 100;
const int INF = 999999999;
const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
using namespace std;

int n;
int color[MAX_N];
int adj[MAX_N][MAX_N];
int d[MAX_N], p[MAX_N];

int prim(void) {
    int u, minv;

    for (int i = 0; i < n; i++) {
        color[i] = WHITE;
        d[i] = INF;
        p[i] = -1;
    }

    d[0] = 0;
    while (1) {
        minv = INF;
        u = -1;
        for (int i = 0; i < n; i++) {
            if (minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }
        if (minv == INF) break;

        color[u] = BLACK;
        for (int v = 0; v < n; v++) {
            if (color[v] != BLACK && adj[u][v] != INF) {
                if (d[v] > adj[u][v]) {
                    d[v] = adj[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }

    int sum = 0;
    for (int i = 0; i < n; i++) {
        if (p[i] != -1) sum += adj[i][p[i]];
    }

    return sum;
}

int main(void) {
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int v; cin >> v;
            if (v == -1) adj[i][j] = INF;
            else adj[i][j] = v;
        }
    }

    cout << prim() << endl;
    return 0;
}

C++: #include <bits/stdc++.h>
/*
5 6
1 2 5
2 3 8
3 4 1
4 5 2
2 5 3
2 4 6

5 6
1 3 4
1 4 3
3 4 5
2 4 1
2 5 2
4 5 6

5 6
0 2 23
0 3 1
2 3 6
3 1 8
1 4 5
3 4 1
*/

using namespace std;
const int maxn = 1e5 + 10;
int n , m;
vector <int> comp [ maxn ];
int num[ maxn ];
int ans = 0;
pair <int , pair < int , int > > edge [ maxn ];

void merge ( int x , int y ){
	if ( comp [ y ].size() < comp [ x ].size() ){
		//cout << "size of " << x << " = "<< comp [ x ].size() << "  " << "|| size of " << y << " = "<< comp [ y ].size() << endl;
		for ( int i = comp [ y ].size() - 1 ; i >= 0 ; i-- ){
			//cout << comp [ y ][ i ] << " " << comp [ x ][ i ] << " ";
			comp [ x ].push_back( comp [ y ][ i ] );
			comp [ y ].pop_back();
			num [ comp [ y ][ i ] ] = num [ comp [ x ][ 0 ] ];
		}
		//cout <<endl;
		/*
		cout << "rasha_e moalefe1 = ";
		for (int i = 0 ; i < comp [ x ].size() ; i++ ){
			cout << comp [ x ][ i ] << " ";
		}
		cout <<endl;
		*/
	}
	else{
		//cout << "size of " << y << " = "<< comp [ y ].size() << "  " << "|| size of " << x << " = "<< comp [ x ].size() << endl;
		for ( int i = comp [ x ].size() - 1 ; i >= 0 ; i-- ){
			//cout << comp [ x ][ i ] << " " << comp [ y ][ i ] << " ";
			comp [ y ].push_back( comp [ x ][ i ] );
			comp [ x ].pop_back();
			num [ comp [ x ][ i ] ] = num [ comp [ y ][ 0 ] ];
		}
		//cout <<endl;
		/*
		cout << "rasha_e moalefe2 = ";
		for (int i = 0 ; i < comp [ y ].size() ; i++ ){
			cout << comp [ y ][ i ] << " ";
		}
		cout <<endl;
		*/
	}
}

int main (){
	cin >> n >> m;
	for ( int i = 0 ; i < m ; i++ ){
		cin >> edge [ i ].second.first >> edge [ i ].second.second >> edge [ i ].first;
	}
	sort ( edge , edge + m );
	for ( int i = 0 ; i <= n ; i++ ){
		num [ i ] = i;
		comp [ i ].push_back ( i );
	}
	for ( int i = 0 ; i <= m ; i++ ){
		//cout << edge [ i ].second.first << " " << edge [ i ].second.second << endl;
		//cerr <<"i= " << i << "   " << num [ edge [ i ].second.first ] <<" "<< num [ edge [ i ].second.second ] << endl;
		//cerr << endl;
		if ( num [ edge [ i ].second.first ] != num [ edge [ i ].second.second ] ){
			//cerr << endl;
			//cerr <<"i= " << i << "   " << num [ edge [ i ].second.first ] <<" "<< num [ edge [ i ].second.second ] << endl;
			ans += edge [ i ].first;
			//cout << ans << " " << edge [ i ].second.first << " " << edge [ i ].second.second << endl;
			//cerr << endl;
			merge ( num [ edge [ i ].second.first ]  , num [ edge [ i ].second.second ] );
			//cerr <<"i= " << i << "   " << num [ edge [ i ].second.first ] <<" "<< num [ edge [ i ].second.second ] << endl;
		}
	}
	/*
	for ( int i = 1 ; i <= n ; i++ ){
		cout << num [ i ] << " ";
	}
	*/
	cout << ans;
}

C++: #include <iostream>
#include <cstring>
#define INF 2000
using namespace std;

int graph[105][105],n,closest[105],color[105],p[105];
int sum=0;
void prim(){
    int i,j;
    while(1){
        int v=-1,minv=INF;
        for(i=0;i<n;i++){
            if(minv>closest[i]&&color[i]!=1){
                minv=closest[i];
                v=i;
            }
        }
        if(v==-1)break;
        color[v]=1;
        closest[v]=INF;
        for(i=0;i<n;i++){
            if(color[i]!=1&&graph[v][i]<closest[i]&&graph[v][i]!=-1){
                closest[i]=graph[v][i];
                p[i]=v;
            }
        }
    }

    for(i=1;i<n;i++){
        if(p[i]!=-1)sum+=graph[i][p[i]];
    }
}

int main()
{
    memset(color,0,sizeof(color));
    memset(graph,-1,sizeof(graph));
    cin>>n;
    int i,j;
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            cin>>graph[i][j];
        }
    }
    for(i=0;i<n;i++){
        p[i]=-1;
        closest[i]=INF;
    }
    closest[0]=0;
    prim();
    cout<<sum<<endl;
    return 0;
}