Java中如何对数组进行快速排序

public class QuickSort {

    public static void quickSort(int[] arr, int low, int high) {
        if (low < high) {
            int partitionIndex = partition(arr, low, high);

            quickSort(arr, low, partitionIndex - 1);
            quickSort(arr, partitionIndex + 1, high);
        }
    }

    private static int partition(int[] arr, int low, int high) {
        int pivot = arr[high];
        int i = (low - 1); // Index of smaller element
        for (int j = low; j < high; j++) {
            // If current element is smaller than or equal to pivot
            if (arr[j] <= pivot) {
                i++;

                // swap arr[i] and arr[j]
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }

        // swap arr[i+1] and arr[high] (or pivot)
        int temp = arr[i + 1];
        arr[i + 1] = arr[high];
        arr[high] = temp;

        return i + 1;
    }

    public static void main(String[] args) {
        int[] arr = {10, 7, 8, 9, 1, 5};
        int n = arr.length;
        quickSort(arr, 0, n - 1);

        System.out.println("Sorted array:");
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
}

private static int partition(int[] arr, int low, int high) {
    // 三数取中
    int mid = low + (high - low) / 2;
    int pivot = medianOfThree(arr, low, mid, high);

    // 将基准值放到high位置
    swap(arr, pivot, high);

    pivot = arr[high];
    int i = (low - 1); // Index of smaller element
    for (int j = low; j < high; j++) {
        // If current element is smaller than or equal to pivot
        if (arr[j] <= pivot) {
            i++;

            // swap arr[i] and arr[j]
            swap(arr, i, j);
        }
    }

    // swap arr[i+1] and arr[high] (or pivot)
    swap(arr, i + 1, high);

    return i + 1;
}

private static int medianOfThree(int[] arr, int a, int b, int c) {
    if ((arr[a] - arr[b]) * (arr[c] - arr[a]) >= 0) {
        return a;
    } else if ((arr[b] - arr[a]) * (arr[c] - arr[b]) >= 0) {
        return b;
    } else {
        return c;
    }
}

private static void swap(int[] arr, int i, int j) {
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}

private static void quickSort(int[] arr, int low, int high) {
    int INSERTION_SORT_THRESHOLD = 10; // 阈值

    if (high - low + 1 < INSERTION_SORT_THRESHOLD) {
        insertionSort(arr, low, high);
    } else if (low < high) {
        int partitionIndex = partition(arr, low, high);

        quickSort(arr, low, partitionIndex - 1);
        quickSort(arr, partitionIndex + 1, high);
    }
}

private static void insertionSort(int[] arr, int low, int high) {
    for (int i = low + 1; i <= high; i++) {
        int key = arr[i];
        int j = i - 1;

        /* Move elements of arr[0..i-1], that are
           greater than key, to one position ahead
           of their current position */
        while (j >= low && arr[j] > key) {
            arr[j] = arr[j + 1];
            j = j - 1;
        }
        arr[j + 1] = key;
    }
}