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Heap sort #4

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May 2, 2024
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85 changes: 85 additions & 0 deletions Java/Algorithm/SortingAlgorithm/Heap sort
Original file line number Diff line number Diff line change
@@ -0,0 +1,85 @@
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Scanner;

public class HeapSort {

// Function to perform heap sort
public static void heapSort(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[]
public static 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);
}
}

public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);

try {
System.out.print("Enter the number of elements: ");
int n = scanner.nextInt();
if (n <= 0) {
throw new IllegalArgumentException("Number of elements must be positive.");
}

int[] arr = new int[n];

System.out.println("Enter the elements:");
for (int i = 0; i < n; i++) {
arr[i] = scanner.nextInt();
}

System.out.println("Original array: " + Arrays.toString(arr));

heapSort(arr);

System.out.println("Sorted array: " + Arrays.toString(arr));
} catch (InputMismatchException e) {
System.out.println("Invalid input. Please enter integers only.");
} catch (IllegalArgumentException e) {
System.out.println(e.getMessage());
} finally {
scanner.close();
}
}
}