heapsort.java

heapsort.java

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+// Java program for implementation of Heap Sort
+public class HeapSort {
+	public void sort(int arr[])
+	{
+		int n = arr.length;
+
+		// 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
+			int temp = arr[0];
+			arr[0] = arr[i];
+			arr[i] = temp;
+
+			// call max heapify on the reduced heap
+			heapify(arr, i, 0);
+		}
+	}
+
+	// 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) {
+			int swap = arr[i];
+			arr[i] = arr[largest];
+			arr[largest] = swap;
+
+			// Recursively heapify the affected sub-tree
+			heapify(arr, n, largest);
+		}
+	}
+
+	/* A utility function to print array of size n */
+	static void printArray(int arr[])
+	{
+		int n = arr.length;
+		for (int i = 0; i < n; ++i)
+			System.out.print(arr[i] + " ");
+		System.out.println();
+	}
+
+	// Driver program
+	public static void main(String args[])
+	{
+		int arr[] = { 12, 11, 13, 5, 6, 7 };
+		int n = arr.length;
+
+		HeapSort ob = new HeapSort();
+		ob.sort(arr);
+
+		System.out.println("Sorted array is");
+		printArray(arr);
+	}
+}