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>
using namespace std;
static const int MAX = 101;
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, mincost;
    int d[MAX], p[MAX], color[MAX];
     for(int i=0; i<MAX; i++)
     {
         color[i] = WHITE;
         d[i] = INFTY;
         p[i] = -1;
     }
     d[0] = 0;
     while(1)
     {
         mincost = INFTY;
         for(int i=0; i<n; i++)
         {
             if(color[i] != BLACK && d[i] < mincost)
             {
                 mincost = d[i];
                 u = i;
             }
         }
         if(mincost == INFTY)
                break;
         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;
                     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;
     int e;
     for(int i=0; i<n; i++)
     {
         for(int j=0; j<n; j++)
         {
             cin >> e;
             if(e == -1)
                M[i][j] = INFTY;
             else
                M[i][j] = e;
         }
     }
     cout << prim() << endl;
     return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

using Weight = int;
struct Edge {
    int src, dst;
    Weight weight;
    Edge(int src_, int dst_, int weight_) :
        src(src_), dst(dst_), weight(weight_) { }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
typedef vector<Weight> Array;
typedef vector<Array> Matrix;

bool operator < (const Edge &e, const Edge &f){ return e.weight > f.weight; }
pair<Weight, Edges> prim(const Graph &g, int r = 0) {
    Edges T; Weight total = 0; vector<int> vis(g.size());
    priority_queue<Edge> q;
    q.emplace(-1, r, 0);
    while (!q.empty()) {
        Edge e = q.top(); q.pop();
        if (vis[e.dst]) continue;
        vis[e.dst] = true;
        total += e.weight; if(e.src != -1) T.push_back(e);
        for(auto& f : g[e.dst]) if (!vis[f.dst]) q.push(f);
    }
    return make_pair(total, T);
}

int main(){
    int n;
    cin >> n;
    Graph g(n);
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            int x;
            cin >> x;
            if(x != -1) g[i].emplace_back(i,j,x);
        }
    }
    cout << prim(g).first << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;

const int INF = numeric_limits<int>::max();

struct Graph {
    enum Color {WHITE, GRAY, BLACK};
    vector<vector<int>> cost;
    vector<Color> color;
    vector<int> mincost;
    Graph(int n) {
        cost.assign(n, vector<int>(n, INF));
        color.assign(n, WHITE);
        mincost.assign(n, INF);
    }
};

int main()
{
    int n;
    cin >> n;
    Graph g(n);
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> g.cost[i][j];
            g.cost[i][j] = g.cost[i][j] == -1 ? INF : g.cost[i][j];
        }
    }
    
    int ans = 0;

    // Prim
    g.mincost[0] = 0;
    while (true) {
        int u = -1;
        for (int v = 0; v < n; v++) {
            if (g.color[v] == Graph::WHITE && (u == -1 || g.mincost[v] < g.mincost[u])) {
                u = v;
            }
        }
        if (u == -1) break;
        g.color[u] = Graph::BLACK;
        ans += g.mincost[u];
        for (int v = 0; v < n; v++) {
            g.mincost[v] = min(g.mincost[v], g.cost[u][v]);
        }
    }
    cout << ans << endl;
}