added heapsort in cpp

Sorting/Heap Sort/cpp/heapsort.cpp

@@ -0,0 +1,68 @@
+// C++ program for implementation of Heap Sort
+#include <iostream>
+
+using namespace std;
+
+// To heapify a subtree rooted with node i which is
+// an index in arr[]. n is size of heap
+void heapify(int arr[], int n, int i)
+{
+    int largest = i; // Initialize largest as root
+    int l = 2*i + 1; // left = 2*i + 1
+    int r = 2*i + 2; // right = 2*i + 2
+
+    // If left child is larger than root
+    if (l < n && arr[l] > arr[largest])
+        largest = l;
+
+    // If right child is larger than largest so far
+    if (r < n && arr[r] > arr[largest])
+        largest = r;
+
+    // If largest is not root
+    if (largest != i)
+    {
+        swap(arr[i], arr[largest]);
+
+        // Recursively heapify the affected sub-tree
+        heapify(arr, n, largest);
+    }
+}
+
+// main function to do heap sort
+void heapSort(int arr[], int n)
+{
+    // Build heap (rearrange array)
+    for (int i = n / 2 - 1; i >= 0; i--)
+        heapify(arr, n, i);
+
+    // One by one extract an element from heap
+    for (int i=n-1; i>=0; i--)
+    {
+        // Move current root to end
+        swap(arr[0], arr[i]);
+
+        // call max heapify on the reduced heap
+        heapify(arr, i, 0);
+    }
+}
+
+/* A utility function to print array of size n */
+void printArray(int arr[], int n)
+{
+    for (int i=0; i<n; ++i)
+        cout << arr[i] << " ";
+    cout << "\n";
+}
+
+// Driver program
+int main()
+{
+    int arr[] = {12, 11, 13, 5, 6, 7};
+    int n = sizeof(arr)/sizeof(arr[0]);
+
+    heapSort(arr, n);
+
+    cout << "Sorted array is \n";
+    printArray(arr, n);
+}