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8.HeapSort.cpp

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+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <cmath>
+#include <iomanip>
+#include <limits>
+#include <vector>
+#include <set>
+#include <map>
+using namespace std;
+typedef unsigned long long ull;
+
+void heapify(int arr[], int n, int i) //  O(lgn)
+{
+    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);
+    }
+}
+
+void heap_sort(int arr[], int n) // O(nlgn) tighter bound
+{
+    // 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);
+    }
+}
+
+int main()
+{
+
+    int a[] = {10, 7, 8, 9, 1, 5, 96, 12, 6, 13};
+
+    heap_sort(a,10); //sorting
+    for(int i=0;i<10; i++)
+        cout << a[i] << " ";
+}
+