heapsort c++

#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

// Skilgreiningar:
void hruga(vector<int>&, int, int);
bool minna(vector<int>&, int, int);
void exchange(vector<int>&, int, int);

void heapsort(vector<int>& v) {
    int n = v.size();
    for (int k=n/2; k>=1; k--)
        hruga(v, k, n);
    while (n > 1) {
        exchange(v, 1, n--);
        hruga(v, 1, n);
    }
}

void hruga(vector<int>& v, int k, int n) {
    while (2*k <= n) {
        int j = 2*k;
        if (j<n && minna(v, j, j+1)) j++;
        if (!minna(v, k, j)) break;
        exchange(v, k, j);
        k = j;
    }
}

bool minna(vector<int>& v, int i, int j) {
    return v[i-1] < v[j-1];
}

void exchange(vector<int>& v, int i, int j) {
    int swap = v[i-1];
    v[i-1] = v[j-1];
    v[j-1] = swap;
}
/////////////////////////////////////////////////////

bool issorted(vector<int>& v) {
    /*
     * Athugar hvort vigurinn v sé í stígandi röð
     */
    cout << endl;
    for (int i = 1; i < v.size(); i++) {
        if (v[i] < v[i - 1]) {
            return false;
        }
    }
    return true;
}

int main() {
    // Prófum sort á vigrum af lengdunum 0, 101, og 1000:
    vector<int> sizes = {0, 101, 1000};
    for (int n : sizes) {
        // Upphafstillum v með tölunum 0 upp í n-1 í slembinni röð
        vector<int> v(n);
        for (int i = 0; i < n; i++) {
            v[i] = i;
        }
        random_shuffle(v.begin(), v.end());

        // Röðum v aftur
        heapsort(v);

        // Athugum hvort röðunin tókst
        if (issorted(v)) {
            cout << "Röðun á " << v.size() << " staka vigri tókst" << endl;
        } else {
            cout << "Röðun á " << v.size() << " staka vigri mistókst" << endl;
        }
    }
}