c#中的MergeSort算法

Question

我在下面写了Merge Class的代码:

class Merge
{

    public static void sort(IComparable[] a)
    {
        sort(a, 0, a.Length);
    }

    public static void sort(IComparable[] a, int low, int high)
    {
        int N = high - low;
        if (N <= 1)
            return;

        int mid = low + N / 2;

        sort(a, low, mid);
        sort(a, mid, high);

        IComparable[] aux = new IComparable[N];
        int i = low, j = mid;
        for (int k = 0; k < N; k++)
        {
            if (i == mid) aux[k] = a[j++];
            else if (j == high) aux[k] = a[i++];
            else if (a[j].CompareTo(a[i]) < 0) aux[k] = a[j++];
            else aux[k] = a[i++];
        }

        for (int k = 0; k < N; k++)
        {
            a[low + k] = aux[k];
        }
    }

    private static Boolean isSorted(IComparable[] a)
    {
        for (int i = 1; i < a.Length; i++)
            if (a[i].CompareTo(a[i - 1]) < 0) return false;
        return true;
    }

}

下面的代码是实现.我认为下面的代码不应该是错的!但它不会编译......

class Program
{
    static void Main(string[] args)
    {
    Merge ms = new Merge();

    Double[] MyArray = { 80,10,52,7,36,7,67,1,8,54 };
    Console.WriteLine("first array is: \n");
    for (int k = 0; k < MyArray.Length; k++)
    {
        Console.Write(MyArray[k]);
        if (k<9)
           Console.Write(" , ");
    }
    ms.sort(MyArray);  // Error is here. Does't compile !!!
    Console.WriteLine("\n");
    Console.WriteLine("\nsorted array is: \n ");
    for (int k = 0; k < MyArray.Length; k++)
    {
        Console.Write(MyArray[k]);
        if (k<9)
           Console.Write(" , ");
    }
    Console.ReadLine();
    }
}

它不会编译.错误在于ms.sort(MyArray);.我究竟做错了什么？请带我...

问候

Answer 1

这段代码有两个问题:

1. 签名不匹配,在这种情况下IComparable[]不直接兼容double[]
2. 您无法sort直接通过实例调用该方法

修复此问题的最小更改量是使方法通用,而Merge.sort不是调用ms.sort.

这是我将如何实现sort:

public static void sort<T>(T[] a)
    where T : IComparable<T>
{
    sort(a, 0, a.Length);
}

public static void sort<T>(T[] a, int low, int high)
    where T : IComparable<T>
{
    int N = high - low;
    if (N <= 1)
        return;

    int mid = low + N / 2;

    sort(a, low, mid);
    sort(a, mid, high);

    T[] aux = new T[N];
    int i = low, j = mid;
    for (int k = 0; k < N; k++)
    {
        if (i == mid) aux[k] = a[j++];
        else if (j == high) aux[k] = a[i++];
        else if (a[j].CompareTo(a[i]) < 0) aux[k] = a[j++];
        else aux[k] = a[i++];
    }

    for (int k = 0; k < N; k++)
    {
        a[low + k] = aux[k];
    }
}

请注意,我改为使用T而不是IComparable,并添加了一个约束,说我们需要一个T实现IComparable<T>.

此外,更改您的通话:

ms.sort(...);

对此:

Merge.sort(...);

Answer 2

    //merge sort recurcive

    public void MergeSort(int[] input,int startIndex,int endIndex)
    {
        int mid;

        if (endIndex > startIndex)
        {
            mid = (endIndex + startIndex) / 2;
            MergeSort(input, startIndex, mid);
            MergeSort(input, (mid + 1), endIndex);
            Merge(input, startIndex, (mid + 1), endIndex);
        }
    }

    public void Merge(int[] input, int left, int mid, int right)
    {
        //Merge procedure takes theta(n) time
        int[] temp = new int[input.Length];
        int i, leftEnd,lengthOfInput,tmpPos;
        leftEnd = mid - 1;
        tmpPos = left;
        lengthOfInput = right - left + 1;

        //selecting smaller element from left sorted array or right sorted array and placing them in temp array.
        while ((left <= leftEnd) && (mid <= right))
        {
            if (input[left] <= input[mid])
            {
                temp[tmpPos++] = input[left++];
            }
            else
            { 
                temp[tmpPos++]=input[mid++];
            }
        }
        //placing remaining element in temp from left sorted array
        while (left <= leftEnd)
        {
            temp[tmpPos++] = input[left++];
        }

        //placing remaining element in temp from right sorted array
        while (mid <= right)
        {
            temp[tmpPos++] = input[mid++];
        }

        //placing temp array to input
        for (i = 0; i < lengthOfInput;i++ )
        {
            input[right]=temp[right];
            right--;
        }
    }

     int[] input3 = { 22, 4, 6, 0, 9, 12, 156, 86,99};
     MergeSort(input3, 0, input3.Length - 1);
        for (int i = 0; i < input3.Length; i++)
            Console.Write(input3[i]+", ");
        Console.WriteLine("");