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56 lines (46 loc) · 1.55 KB
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// Heap Sort Algorithm in Java
// Time Complexity: O(n log n)
// Builds a max heap and repeatedly extracts the largest element.
public class HeapSort {
public static void sort(int[] arr) {
int n = arr.length;
// Build max heap
for (int i = n / 2 - 1; i >= 0; i--)
heapify(arr, n, i);
// Extract elements one by one
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 reduced heap
heapify(arr, i, 0);
}
}
// Heapify subtree rooted at index i
private 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) {
int[] data = {12, 11, 13, 5, 6, 7};
sort(data);
for (int num : data)
System.out.print(num + " ");
}
}