package chap9;

public class Sorting
{
    //选择排序
    public static <T extends Comparable<T>>
    void selectionSort(T[] data)
    {
        int min;
        T temp;

        for (int index = 0; index < data.length-1; index++)
        {
            min = index;
            for (int scan = index+1; scan < data.length; scan++)
                if (data[scan].compareTo(data[min])<0)
                    min = scan;

            swap(data, min, index);
        }
    }

    //互换
    private static <T extends Comparable<T>>
    void swap(T[] data, int index1, int index2)
    {
        T temp = data[index1];
        data[index1] = data[index2];
        data[index2] = temp;
    }

    //插入排序
    public static <T extends Comparable<T>>
    void insertionSort(T[] data)
    {
        for (int index = 1; index < data.length; index++)
        {
            T key = data[index];
            int position = index;

            // shift larger values to the right
            while (position > 0 && data[position-1].compareTo(key) > 0)
            {
                data[position] = data[position-1];//把数值大的数换到了右边
                position--;//position变成左边数的索引
            }

            data[position] = key;
        }
    }

    //冒泡排序
    public static <T extends Comparable<T>>
    void bubbleSort(T[] data)
    {
        int position, scan;
        T temp;

        for (position =  data.length - 1; position >= 0; position--)
        {
            for (scan = 0; scan <= position - 1; scan++)
            {
                if (data[scan].compareTo(data[scan+1]) > 0)
                    swap(data, scan, scan + 1);
            }//第一个循环里面是第一次两个两个比较到列表末尾
        }//第二个循环里面是一共进行内循环的次数，其次数与列表元素个数-1相等
    }


    public static <T extends Comparable<T>>
    void mergeSort(T[] data)
    {
        mergeSort(data, 0, data.length - 1);
    }


    private static <T extends Comparable<T>>
    void mergeSort(T[] data, int min, int max)
    {
        if (min < max)
        {
            int mid = (min + max) / 2;
            mergeSort(data, min, mid);
            mergeSort(data, mid+1, max);
            merge(data, min, mid, max);
        }
    }


    @SuppressWarnings("unchecked")
    private static <T extends Comparable<T>>
    void merge(T[] data, int first, int mid, int last)
    {
        T[] temp = (T[])(new Comparable[data.length]);

        int first1 = first, last1 = mid;  // endpoints of first subarray第一个子数组的端点
        int first2 = mid+1, last2 = last;  // endpoints of second subarray第二个子数组的端点
        int index = first1;  // next index open in temp array

        //  Copy smaller item from each subarray into temp until one
        //  of the subarrays is exhausted
        while (first1 <= last1 && first2 <= last2)
        {
            if (data[first1].compareTo(data[first2]) < 0)
            {
                temp[index] = data[first1];
                first1++;
            }
            else
            {
                temp[index] = data[first2];
                first2++;
            }
            index++;
        }

        //  Copy remaining elements from first subarray, if any
        while (first1 <= last1)
        {
            temp[index] = data[first1];
            first1++;
            index++;
        }

        //  Copy remaining elements from second subarray, if any
        while (first2 <= last2)
        {
            temp[index] = data[first2];
            first2++;
            index++;
        }

        //  Copy merged data into original array
        for (index = first; index <= last; index++)
            data[index] = temp[index];
    }

    //快速排序法
    public static <T extends Comparable<T>>
    void quickSort(T[] data)
    {
        quickSort(data, 0, data.length - 1);
    }


    private static <T extends Comparable<T>>
    void quickSort(T[] data, int min, int max)
    {
        if (min < max)
        {
            // create partitions
            int indexofpartition = partition(data, min, max);

            // sort the left partition (lower values)
            quickSort(data, min, indexofpartition - 1);

            // sort the right partition (higher values)
            quickSort(data, indexofpartition + 1, max);
        }
    }


    private static <T extends Comparable<T>>
    int partition(T[] data, int min, int max)
    {
        T partitionelement;
        int left, right;
        int middle = (min + max) / 2;

        // use the middle data value as the partition element
        partitionelement = data[middle];
        // move it out of the way for now
        swap(data, middle, min);

        left = min;
        right = max;

        while (left < right)
        {
            // search for an element that is > the partition element
            while (left < right && data[left].compareTo(partitionelement) <= 0)
                left++;

            // search for an element that is < the partition element
            while (data[right].compareTo(partitionelement) > 0)
                right--;

            // swap the elements
            if (left < right)
                swap(data, left, right);
        }

        // move the partition element into place
        swap(data, min, right);

        return right;
    }
}