added heap sort in cpp (#54)

* add binary search in js

* added merge sort in c

* added quick sort in cpp

* modified quick sort

* added heap sort

* updated readme.md

sorting/README.md

@@ -7,6 +7,7 @@
 3. [Selection Sort](c-or-cpp/selection-sort.cpp)
 4. [Merge Sort](c-or-cpp/merge-sort.c)
 5. [Quick Sort](c-or-cpp/quick-sort.cpp)
+6. [Heap Sort](c-or-cpp/heap-sort.cpp)
 
 ### C#
 

sorting/c-or-cpp/heap-sort.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+using namespace std;
+void heapify(int a[], int n, int i);
+void heapSort(int a[], int n);
+
+// Driver code
+int main()
+{
+    cout << "Enter the length of array" << endl;
+    int n;
+    cin >> n;
+    int *a = new int(n);
+    // Getting elements of array
+    cout << "Enter the elements of array" << endl;
+    for (int i = 0; i < n; i++)
+        cin >> a[i];
+    cout << "Original array:\n";
+    for (int i = 0; i < n; i++)
+        cout << a[i] << " ";
+    heapSort(a, n);
+    cout << "\nSorted array:\n";
+    for (int i = 0; i < n; i++)
+        cout << a[i] << " ";
+    delete (a);
+    return 0;
+}
+
+// To heapify a subtree rooted with node i which is an index in a[]
+void heapify(int a[], int n, int i)
+{
+    int largest = i;   // Initialize largest as root
+    int l = 2 * i + 1; 
+    int r = 2 * i + 2; 
+
+    // If left child is larger than root
+    if (l < n && a[l] > a[largest])
+        largest = l;
+
+    // If right child is larger than largest so far
+    if (r < n && a[r] > a[largest])
+        largest = r;
+
+    // If largest is not root
+    if (largest != i)
+    {
+        swap(a[i], a[largest]);
+        // Recursively heapify the affected sub-tree
+        heapify(a, n, largest);
+    }
+}
+
+
+void heapSort(int a[], int n)
+{
+    // Build heap (rearrange array)
+    for (int i = n / 2 - 1; i >= 0; i--)
+        heapify(a, n, i);
+    // One by one extract an element from heap
+    for (int i = n - 1; i > 0; i--)
+    {
+        // Move current root to end
+        swap(a[0], a[i]);
+        // call max heapify on the reduced heap
+        heapify(a, i, 0);
+    }
+}