Go: package main

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

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

C++: #include <bits/stdc++.h>
 
using namespace std;
namespace kruskal_n {
struct UnionFind {
	int sz;
	vector<int> par;
	UnionFind(int a) : sz(a), par(sz, -1) {}
	int root(int x) { return par[x] < 0 ? x : par[x] = root(par[x]);}
	bool same(int x, int y) { return root(x) == root(y);}
	bool unite(int x, int y) {
		x = root(x);
		y = root(y);
		if (x == y) return false;
		if (size(x) < size(y)) swap(x, y);
		par[x] += par[y];
		par[y] = x;
		return true;
	}
	int size(int x) { return -par[root(x)];}
	int size() { return sz;}
};
template<class W>
struct Edge {
	using type = Edge<W>;
	int from;
	int to;
	W w;
	template<class... Args> Edge(int f, int t, Args... args) : from(f), to(t), w(args...) {}
	inline bool operator<(const Edge& rhs) const { return w < rhs.w; }
	inline bool operator>(const type& rhs) const { return rhs < *this; }
	inline bool operator>=(const type& rhs) const { return !(*this < rhs); }
	inline bool operator<=(const type& rhs) const { return !(rhs < *this); }
	inline bool operator==(const type& rhs) const { return !(*this < rhs) && !(rhs < *this); }
	inline bool operator!=(const type& rhs) const { return (*this < rhs) || (rhs < *this); }
};
template<class W>
struct Edges : private vector<Edge<W>> {
	using type = vector<Edge<W>>;
	Edges() : type() {}
	Edges(int n) : type() {assert(0 && "Constructor must be empty");}
	template<class... Args> void add_edge(int u, int v, Args... args) {
		(*this).emplace_back(u, v, args...);
	}
	using type::begin; using type::end; using type::rbegin; using type::rend;
	using type::cbegin; using type::cend; using type::crbegin; using type::crend;
	using type::size; using type::operator[]; using type::at; using type::back; using type::front;
	using type::reserve; using type::resize; using type::assign; using type::shrink_to_fit;
	using type::clear; using type::erase; using type::insert; using type::swap; 
	using type::push_back; using type::pop_back; using type::emplace_back; using type::empty;
};
template<class T>
T Kruskal(Edges<T>& e) {
	sort(e.begin(), e.end());
	UnionFind u(e.size());
	T res = 0;
	for (auto &x : e) {
		if (u.unite(x.from, x.to)) res += x.w;
	}
	return res;
}
}
using kruskal_n::Kruskal;
template<class T> using graph = kruskal_n::Edges<T>;

int main() {
    int n; cin >> n;
    graph<long long> g;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int c; cin >> c;
            if (c >= 0) g.add_edge(i, j, c);
        }
    }
    cout << Kruskal(g) << endl;
}

C++: #include <climits>
#include <iostream>
#include <vector>

using namespace std;

int prim(vector<vector<int>>& graph) {
    int n = graph.size() - 1;
    vector<bool> isInTree(n + 1);
    vector<int> weight(n + 1);
    for (int i = 1; i <= n; i++)
        weight[i] = INT_MAX;
    int v = 1;
    weight[v] = 0;
    while (true) {
        isInTree[v] = true;
        int minCost = INT_MAX;
        for (int i = 1; i <= n; i++) {
            if (!isInTree[i])
                continue;
            for (int j = 1; j <= n; j++) {
                int cost = graph[i][j];
                if (cost >= 0 && !isInTree[j] && cost <= minCost) {
                    v = j;
                    minCost = cost;
                }
            }
        }
        if (minCost == INT_MAX)
            break;
        weight[v] = minCost;
    }

    int result = 0;
    for (int i = 1; i <= n; i++)
        result += weight[i];
    return result;
}

int main() {
    int n;
    cin >> n;
    vector<vector<int>> graph(n + 1, vector<int>(n + 1));
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            cin >> graph[i][j];

    int totalCost = prim(graph);
    cout << totalCost << endl;

    return 0;
}

C++: a