算法导论_堆排序

package com.wzs;import java.util.Arrays;/** * 算法导论--page86 *  * @author Administrator *  */public class HeapSort {private static int[] sort = new int[] { 1, 0, 10, 20, 3, 5, 6, 4, 9, 8, 12, 17, 34, 11 };public static void main(String[] args) {System.out.println(Arrays.toString(sort));buildMaxHeap(sort);System.out.println(Arrays.toString(sort));heapSort(sort);System.out.println(Arrays.toString(sort));}/** * 建堆 *  * @param data */private static void buildMaxHeap(int[] data) {// 没有子节点的才需要创建最大堆，从最后一个的父节点开始int startIndex = getParentIndex(data.length - 1);// 从尾端开始创建最大堆，每次都是正确的堆for (int i = startIndex; i >= 0; i--) {maxHeap(data, data.length, i);}}/** * 维护堆的性质 *  * @param data * @param heapSize *            需要创建最大堆的大小，一般在sort的时候用到，因为最多值放在末尾，末尾就不再归入最大堆了 * @param index *            当前需要创建最大堆的位置 */private static void maxHeap(int[] data, int heapSize, int index) {// 当前点与左右子节点比较int left = getChildLeftIndex(index);int right = getChildRightIndex(index);int largest = index;if (left < heapSize && data[index] < data[left]) {largest = left;}if (right < heapSize && data[largest] < data[right]) {largest = right;}// 得到最大值后可能需要交换，如果交换了，其子节点可能就不是最大堆了，需要重新调整if (largest != index) {exchange(data, index, largest);maxHeap(data, heapSize, largest);}}private static void exchange(int[] arr, int i, int j) {int temp = arr[i];arr[i] = arr[j];arr[j] = temp;}/** * 排序，最大值放在末尾，data虽然是最大堆，在排序后就成了递增的 *  * @param data */private static void heapSort(int[] data) {// 末尾与头交换，交换后调整最大堆for (int i = data.length - 1; i > 0; i--) {int temp = data[0];data[0] = data[i];data[i] = temp;maxHeap(data, i, 0);}}/** * 父节点位置 *  * @param current * @return */private static int getParentIndex(int current) {return (current - 1) >> 1;}/** * 左子节点position 注意括号，加法优先级更高 *  * @param current * @return */private static int getChildLeftIndex(int current) {return (current << 1) + 1;}/** * 右子节点position *  * @param current * @return */private static int getChildRightIndex(int current) {return (current << 1) + 2;}}