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HeapSort.java
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HeapSort.java
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/**
* HeapSort: a sort algorithm based on max heap, where the largest item is
* stored at the root of the heap.
*
* Time Complexity: O(Logn).
* Space Complexity: O(n).
*
*/
import java.util.Arrays;
/**
* http://www.geeksforgeeks.org/heap-sort/
*/
public class HeapSort {
public static void sort(int[] arr) {
int n = arr.length;
for (int i = n/2 - 1; i >= 0; i--)
heapify(arr, n, i);
for (int i=n-1; i>=0; i--) {
swap(arr, 0, i);
heapify(arr, i, 0);
}
}
private static void heapify(int arr[], int n, int i) {
int largest = i;
int l = 2*i + 1;
int r = 2*i + 2;
if (l < n && arr[l] > arr[largest]) largest = l;
if (r < n && arr[r] > arr[largest]) largest = r;
if (largest != i) {
swap(arr, i, largest);
heapify(arr, n, largest);
}
}
private static void swap(int[] nums, int i, int j) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
public static void main(String[] args) {
int[] arr1 = {10, 3, 7, 5, 20, 15, 1};
HeapSort.sort(arr1);
System.out.println(Arrays.toString(arr1));
int[] arr2 = {};
HeapSort.sort(arr2);
System.out.println(Arrays.toString(arr2));
int[] arr3 = {10};
HeapSort.sort(arr3);
System.out.println(Arrays.toString(arr3));
}
}