排序 堆排序

public class HeapSort {    static class ArrayUtils {        public static void printArray(int[] array) {            System.out.print("{");            for (int i = 0; i < array.length; i++) {                System.out.print(array[i]);                if (i < array.length - 1) {                    System.out.print(", ");                }            }            System.out.println("}");        }        public static void exchangeElements(int[] array, int index1, int index2) {            int temp = array[index1];            array[index1] = array[index2];            array[index2] = temp;        }    }    public static void main(String[] args) {        int[] array = { 9, 8, 13, 7, 6, 5, 4, 3, 2, 1, 0, -1, -2, -3, 12, 11, 15, 14 };        System.out.println("Before heap:");        ArrayUtils.printArray(array);        heapSort(array);        System.out.println("After heap sort:");        ArrayUtils.printArray(array);    }    public static void heapSort(int[] array) {//      if (array == null || array.length <= 1) {//          return;//      }        buildMaxHeap(array);        for (int i = array.length - 1; i >= 1; i--) {            ArrayUtils.exchangeElements(array, 0, i);            maxHeap(array, i, 0);        }    }    private static void buildMaxHeap(int[] array) {//      if (array == null || array.length <= 1) {//          return;//      }        int half = (array.length) / 2;        for (int i = half; i >= 0; i--) {            maxHeap(array, array.length, i);        }    }    // 堆调整，使其生成最大堆    private static void maxHeap(int[] array, int heapSize, int index) {        int left = index * 2 + 1;// 左子节点索引        int right = index * 2 + 2;// 右子节点索引        int largest = index;// 最大节点索引        // 如果左子节点大于父节点，则将左子节点作为最大节点        if (left < heapSize && array[left] > array[index]) {            largest = left;        }        // 如果右子节点比最大节点还大，那么最大节点应该是右子节点        if (right < heapSize && array[right] > array[largest]) {            largest = right;        }        // 最后，如果最大节点和父节点不一致，则交换他们的值        if (index != largest) {            ArrayUtils.exchangeElements(array, index, largest);            // 交换完父节点和子节点的值，对换了值的子节点检查是否符合最大堆的特性            maxHeap(array, heapSize, largest);        }        ArrayUtils.printArray(array);    }    public static void maxHeaps(int[] array,int heapSize,int index){        if(array==null || array.length<=1){            return;        }        int left = 2*index+1;        int right = 2*index+2;        int largest = index;        if(left<heapSize && array[left]>array[index]){            largest=left;        }        if(right<heapSize && array[right]>array[largest]){            largest=right;        }        if(index!=largest){            ArrayUtils.exchangeElements(array, index, largest);            maxHeaps(array, heapSize, largest);        }    }}