heap-sort.cpp

/* Heap sort in c++ */

#include <iostream>
 
using namespace std;
 
// A function to heapify the array.
void MaxHeapify(int a[], int i, int n)
{
	int j, temp;
	temp = a[i];
	j = 2*i;
 
 	while (j <= n)
	{
		if (j < n && a[j+1] > a[j])
		j = j+1;
		// Break if parent value is already greater than child value.
		if (temp > a[j])
			break;
		// Switching value with the parent node if temp < a[j].
		else if (temp <= a[j])
		{
			a[j/2] = a[j];
			j = 2*j;
		}
	}
	a[j/2] = temp;
	return;
}
void HeapSort(int a[], int n)
{
	int i, temp;
	for (i = n; i >= 2; i--)
	{
		// Storing maximum value at the end.
		temp = a[i];
		a[i] = a[1];
		a[1] = temp;
		// Building max heap of remaining element.
		MaxHeapify(a, 1, i - 1);
	}
}
void Build_MaxHeap(int a[], int n)
{
	int i;
	for(i = n/2; i >= 1; i--)
		MaxHeapify(a, i, n);
}
int main()
{
	int n, i;
	cout<<"\nEnter the number of data element to be sorted: ";
	cin>>n;
	n++;
	int* arr = new int[n];
	for(i = 1; i < n; i++)
	{
		cout<<"Enter element "<<i<<": ";
		cin>>arr[i];
	}
	// Building max heap.
	Build_MaxHeap(arr, n-1);
	HeapSort(arr, n-1);
 
	// Printing the sorted data.
	cout<<"\nSorted Data ";
 
	for (i = 1; i < n; i++)
		cout<<"->"<<arr[i];
    cout<<"\nTime Complexity: Best case = Avg case = Worst case = O(n logn)";
 
	return 0;
}

/* Runtime test case:-

Enter the number of data elements to be sorted: 7
Enter element 1: 10
Enter element 2: 8
Enter element 3: 12
Enter element 4: 1
Enter element 5: 2
Enter element 6: 0
Enter element 7: 15

Sorted Data ->0->1->2->8->10->12->15
Time Complexity: Best case = Avg case = Worst case = O(n logn) */