算法之排序：堆排序

Posted 2021-01-25 a154627

public static void swap(int[] arr, int i, int j) {
		int tmp = arr[i];
		arr[i] = arr[j];
		arr[j] = tmp;
	}

	public static void heapInsert(int[] arr, int index) {
		while (arr[index] > arr[(index - 1) / 2]) {
			swap(arr, index, (index - 1) / 2);
			index = (index - 1) / 2;
		}
	}

	public static void heapify(int arr[], int index, int size) {

		while (index * 2 + 1 <= size) {
			int left = index * 2 + 1;
			int right = left + 1;
			int largest = right <= size && arr[right] > arr[left] ? right : left;
			largest = arr[largest] > arr[index] ? largest : index;
			if (largest == index) {
				break;
			}
			swap(arr,largest,index);
			index=left;
		}
	}

	public static void heapSort(int arr[]) {
		if (arr == null || arr.length < 2) {
			return;
		}
		for (int i = 0; i < arr.length; i++) {
			heapInsert(arr, i);
		}
		int size = arr.length-1;
		while (size > 0) {
			swap(arr, 0, size--);
			heapify(arr, 0, size);
		}
	}