Java 堆排序

思路

1. 从最后的非叶子节点开始，从后向前构建一个堆(大顶堆/小顶堆)；即最后的非叶子节点和其下的叶子节点构成一个大顶堆，然后再找前面一个非叶子节点继续
2. 此时根节点是最大的数据，然后将根节点和最后一位进行交换
3. 交换后，排除最后一位最大值，再从根节点开始构建大顶堆
4. 重复2，3步骤

代码

    /**
     * 堆排序
     *
     * @param originArr 需要排序的数组
     * @param isMaxHop  true:从小到大排序，false:从大到小排序
     */
    public static void heapSort(int[] originArr, boolean isMaxHop) {
        if (originArr == null || originArr.length == 0) {
            return;
        }
        // 构建堆
        createHeap(originArr, isMaxHop);
        // 循环2，3步
        for (int i = originArr.length - 1; i >= 1; i--) {
            // 交换
            exchangeElement(originArr, 0, i);
            // 重新构建
            heap(originArr, 0, i, isMaxHop);
        }
    }

    private static void createHeap(int[] originArr, boolean isMaxHop) {
        int half = originArr.length / 2;
        for (int i = half; i >= 0; i--) {
            heap(originArr, i, originArr.length, isMaxHop);
        }
    }

    private static void heap(int[] originArr, int rootIndex, int length, boolean isMax) {
        int leftLeafIndex = rootIndex * 2 + 1;
        int rightLeafIndex = rootIndex * 2 + 2;
        int index = rootIndex;
        if (leftLeafIndex < length && (isMax ? originArr[leftLeafIndex] > originArr[rootIndex] :
                originArr[leftLeafIndex] < originArr[rootIndex])) {
            index = leftLeafIndex;
        }
        if (rightLeafIndex < length && (isMax ? originArr[rightLeafIndex] > originArr[index] :
                originArr[rightLeafIndex] < originArr[index])) {
            index = rightLeafIndex;
        }
        if (rootIndex != index) {
            exchangeElement(originArr, rootIndex, index);
            heap(originArr, index, length, isMax);
        }
    }

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