Java排序算法(五)：堆排序

public class HeapSort {

	public static void main(String[] args) {
		int[] arr = { 6, 5, 3, 1, 8, 7, 2, 4 };
		System.out.println("排序之前：");
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}

		// 堆排序
		heapSort(arr);

		System.out.println();
		System.out.println("排序之后：");
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}
	}

	/**
	 * 堆排序
	 */
	private static void heapSort(int[] arr) { 
		for (int i = arr.length / 2; i >= 0; i--){ // 将待排序的序列构建成一个大顶堆
			heapAdjust(arr, i, arr.length); 
		}
		for (int i = arr.length - 1; i > 0; i--) { // 逐步将每个最大值的根节点与末尾元素交换，并且再调整其成为大顶堆
			swap(arr, 0, i); // 将堆顶记录和当前未经排序子序列的最后一个记录交换
			heapAdjust(arr, 0, i);
		}
	}

	private static void heapAdjust(int[] arr, int i, int n) {
		int child;
		int tmp;
		for (tmp = arr[i]; leftChild(i) < n; i = child) {
			child = leftChild(i);
			if (child != n - 1 && arr[child] < arr[child + 1]) {
				child++;
			}
			if (tmp < arr[child]) {
				arr[i] = arr[child];
			} else {
				break;
			}
		}
		arr[i] = tmp;
	}

	private static int leftChild(int i) {
		return 2 * i + 1;
	}

	private static void swap(int[] arr, int index1, int index2) {
		int tmp = arr[index1];
		arr[index1] = arr[index2];
		arr[index2] = tmp;
	}
}