java堆排序 大堆

//时间复杂度 nLogn

public static void heapSort(int[] array) {
    if (array == null || array.length <= 1) {
        return;
    }
    buildMaxHeap(array);//建立最大堆
    for (int i = array.length - 1; i >= 1; i--) {
        //最大的在0位置，那么开始沉降，这样每交换一次最大的值就丢到最后了
        exchangeElements(array, 0, i);
        //继续获取0位置最大值
        maxHeap(array, i, 0);
    }
}

//(2)     //建立最大堆
private static void buildMaxHeap(int[] array) {
    if (array == null || array.length <= 1) {
        return;
    }
    int half = (array.length-1) / 2;
    for (int i = half; i >= 0; i--) {
        maxHeap(array, array.length, i);
    }
}

private static void maxHeap(int[] array, int heapSize, int index) {
    int left = index * 2 + 1;
    int right = index * 2 + 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) {
        exchangeElements(array, index, largest);

        maxHeap(array, heapSize, largest);
    }
}

private static void exchangeElements(int[] array, int index1, int index2) {
    int temp = array[index1];
    array[index1] = array[index2];
    array[index2] = temp;
}

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("}");
}