Counting the number of comparisons done in Heapsort - c++

Question

I am trying to count the number of comparisons done by heap sorting algorithm.
my code is based on priority queue and I want to know where I should put the counter. here is what I have but when I try to print the counter it shows zero counts, what am I doing wrong? Thank you.
here is the heapbuild function:
#include<iostream>
vector<int> pq_keys;
void buildHeap()
{
int size = pq_keys.size();
int midIdx = (size -2)/2;
while (midIdx >= 0)
{
shiftRight(midIdx, size-1);
--midIdx;
}
and this is the function that does the comparison:
int shiftRight(int low, int high)
{
int root = low;
int counter=0;
while ((root*2)+1 <= high)
{
int leftChild = (root * 2) + 1;
int rightChild = leftChild + 1;
int swapIdx = root;
if (pq_keys[swapIdx] < pq_keys[leftChild])
{
counter++;
cout<<counter;
swapIdx = leftChild;
}
/*If right child exists check if it is less than current root*/
if ((rightChild <= high) && (pq_keys[swapIdx] < pq_keys[rightChild]))
{
counter++;
swapIdx = rightChild;
}
/*Make the biggest element of root, left and right child the root*/
if (swapIdx != root)
{
counter++;
int tmp = pq_keys[root];
pq_keys[root] = pq_keys[swapIdx];
pq_keys[swapIdx] = tmp;
root = swapIdx;
}
else
{
break;
}
}
return counter;
}

Answer 1

You want to increment the counter before you do the comparison. Consider this code, from your shiftRight method:
if (pq_keys[swapIdx] < pq_keys[leftChild])
{
counter++;
cout<<counter;
swapIdx = leftChild;
}
That only increments the counter if the conditional is true. If pq_keys[swpIdx] >= pq_keys[leftChild], then you made the comparison without counting it. You need to change your code to be:
counter++;
if (pq_keys[swapIdx] < pq_keys[leftChild])
{
cout<<counter;
swapIdx = leftChild;
}
You need to do the same thing in the other two places where you count comparisons: increment the counter, then do the comparison.

Answer 2

class LessPredicate
{
size_t callCount_ = 0;
temlate<class T>
bool compare(const T& l, conct T& r)
{
return l < r; // or other logic
}
public:
size_t CallTimes() const { return callCount_; }
temlate<class T>
bool operator() (const T& l, conct T& r)
{
++callCount_;
return compare(l, r);
}
};
int main()
{
LessPredicate less;
...// use it like less(a, b) instead a < b;
auto compareCount = less.CallTimes();
}