Fix bugs and improve code in priorityQueue class

[pratik-dev01]

There are several issues and areas for improvement in the provided C++ implementation of the priorityQueue class:

Bugs and Problems

• The swap function uses pass-by-value, so it does not swap the actual array elements.
• There are inconsistent variable names in deQueue (uses f and r instead of front and rear).
• The class does not initialize size in the constructor, causing isFull() to malfunction.
• The value of INT_MIN is incorrect; use #include <climits> and INT_MIN.
• The heapify function may return an array value instead of void and does not properly maintain heap structure.
• enQueue does not maintain priority order, so it's not a true priority queue.
• Many functions lack error checking and proper handling of edge cases.

Code Improvements

• Implement swap using references or std::swap.
• Ensure correct indexing and use of member variables in all methods.
• Use a min-heap or max-heap to maintain priority order in the queue.
• Return appropriate error codes or throw exceptions instead of using magic numbers.
• Add comments and documentation to clarify logic and usage.

Example Problematic Code

void swap(int a, int b) {
    a = a ^ b;
    b = a ^ b;
    a = a ^ b;
    return;
}
// Should be:
void swap(int &a, int &b) {
    int temp = a;
    a = b;
    b = temp;
}

int deQueue() {
    if(isEmpty()) return INT_MIN; 
    int x = arr[f];
    if(r == f) {
        f++;
        r++;
        return x;
    }
    if(f <= r) 
        f++;
    return x;
}
// Should use front and rear consistently, and update properly.

Please refactor the code to address the above issues. Add tests to confirm correct queue behavior.