C# 实现排序算法

C#实现各种排序

每种排序的要点和实现

C#实现各种排序

文章中参数Func<T, T, bool> comp的意思是：排序后对于任意i < j，不可能有comp(list[j], list[i])

冒泡排序

每次循环都将最值放到最前或者最后
倒着排序，只需访问一次list.Count（可选）
使用sorted布尔变量，如果中途已经排序好了就不用继续排了（可选）
稳定，最值稳定上浮

public static void BubbleSort<T>(IList<T> list)
    where T : IComparable<T>
{
    for (int i = list.Count; i > 0; i--)
    {
        bool sorted = true;
        for (int j = 1; j < i; j++)
        {
            if (list[j].CompareTo(list[j - 1]) < 0)
            {
                T swap = list[j - 1];
                list[j - 1] = list[j];
                list[j] = swap;
                sorted = false;
            }
        }
        if (sorted)
            return;
    }
}
public static void BubbleSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    for (int i = list.Count; i > 0; i--)
    {
        bool sorted = true;
        for (int j = 1; j < i; j++)
        {
            if (comp(list[j], list[j - 1]))
            {
                T swap = list[j - 1];
                list[j - 1] = list[j];
                list[j] = swap;
                sorted = false;
            }
        }
        if (sorted)
            return;
    }
}

选择排序

每次都选出未排序段的最值，加入排序段
倒着排序，只需访问一次list.Count（可选）
不稳定，最值放入排序段时与最值交换的数位置改变

public static void SelectionSort<T>(IList<T> list)
    where T : IComparable<T>
{
    for (int i = list.Count - 1; i > 0; i--)
    {
        int maxIndex = i;
        T maxValue = list[i];
        for (int j = i - 1; j >= 0; j--)
        {
            T value = list[j];
            if (maxValue.CompareTo(value) < 0)
            {
                maxValue = value;
                maxIndex = j;
            }
        }
        T swap = list[i];
        list[i] = list[maxIndex];
        list[maxIndex] = swap;
    }
}
public static void SelectionSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    for (int i = list.Count - 1; i > 0; i--)
    {
        int maxIndex = i;
        T maxValue = list[i];
        for (int j = i - 1; j >= 0; j--)
        {
            T value = list[j];
            if (comp(maxValue, value))
            {
                maxValue = value;
                maxIndex = j;
            }
        }
        T swap = list[i];
        list[i] = list[maxIndex];
        list[maxIndex] = swap;
    }
}

插入排序

将新值插入已排序的一段中
排序段已排序，可以使用二分搜索寻找插入位置（可使用其他方式）
稳定，插入时遇到相同值保持相对位置

public static void InsertionSort<T>(IList<T> list)
    where T : IComparable<T>
{
    int count = list.Count;
    for (int i = 1; i < count; i++)
    {
        T insert = list[i];
        int low = -1, high = i;
        do
        {
            int mid = ((high - low) >> 1) + low;
            if (insert.CompareTo(list[mid]) < 0)
                high = mid;
            else
                low = mid;
        } while (low + 1 != high);
        for (int j = i; j > high; j--)
            list[j] = list[j - 1];
        list[high] = insert;
    }
}
public static void InsertionSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    int count = list.Count;
    for (int i = 1; i < count; i++)
    {
        T insert = list[i];
        int low = -1, high = i;
        do
        {
            int mid = ((high - low) >> 1) + low;
            if (comp(insert, list[mid]))
                high = mid;
            else
                low = mid;
        } while (low + 1 != high);
        for (int j = i; j > high; j--)
            list[j] = list[j - 1];
        list[high] = insert;
    }
}

希尔排序

每次循环结束后，将相隔距离为一个区间的值看作一组，这一组是有序的
区间大小和区间每次缩小的倍数是可以选择的
不稳定，值可能会跳到另一个区间中

public static void ShellSort<T>(IList<T> list)
    where T : IComparable<T>
{
    int count = list.Count;
    int seg = (count >> 1) + 1;
    while (seg > 0)
    {
        for (int i = seg; i < count; i++)
        {
            for (int j = i;
                 j >= seg && list[j].CompareTo(list[j - seg]) < 0;
                 j -= seg)
            {
                T swap = list[j];
                list[j] = list[j - seg];
                list[j - seg] = swap;
            }
        }
        seg /= 2;
    }
}
public static void ShellSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    int count = list.Count;
    int seg = (count >> 1) + 1;
    while (seg > 0)
    {
        for (int i = seg; i < count; i++)
        {
            for (int j = i;
                 j >= seg && comp(list[j], list[j - seg]);
                 j -= seg)
            {
                T swap = list[j];
                list[j] = list[j - seg];
                list[j - seg] = swap;
            }
        }
        seg /= 2;
    }
}

堆排序

数组\(\rightarrow\)堆\(\rightarrow\)已排序的数组
堆是完全二叉树，完全二叉树可以用数组实现
计算机倾向于将相邻地址的值同时载入，索引在数组中跳跃幅度过大，难以利用此功能
不稳定，值在堆中移动，相同的值的相对位置受它们之间的值的影响

public static void HeapSort<T>(IList<T> list)
    where T : IComparable<T>
{
    int i = 0, count = list.Count;
    while (++i < count)
    {
        int j = i;
        int up;
        while (j > 0 && list[up = (j - 1) >> 1].CompareTo(list[j]) < 0)
        {
            T swap = list[up];
            list[up] = list[j];
            list[j] = swap;
            j = up;
        }
    }
    while (--i > 0)
    {
        T swap = list[i];
        list[i] = list[0];
        list[0] = swap;
        int j = 0;
        int down;
        while ((down = (j << 1) + 1) < i)
        {
            if (down + 1 < i && list[down].CompareTo(list[down + 1]) < 0)
                down++;
            if (list[down].CompareTo(list[j]) < 0)
                break;
            swap = list[down];
            list[down] = list[j];
            list[j] = swap;
            j = down;
        }
    }
}
public static void HeapSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    int i = 0, count = list.Count;
    while (++i < count)
    {
        int j = i;
        int up;
        while (j > 0 && comp(list[up = (j - 1) >> 1], list[j]))
        {
            var swap = list[up];
            list[up] = list[j];
            list[j] = swap;
            j = up;
        }
    }
    while (--i > 0)
    {
        var swap = list[i];
        list[i] = list[0];
        list[0] = swap;
        int j = 0;
        int down;
        while ((down = (j << 1) + 1) < i)
        {
            if (down + 1 < i && comp(list[down], list[down + 1]))
                down++;
            if (comp(list[down], list[j]))
                break;
            swap = list[down];
            list[down] = list[j];
            list[j] = swap;
            j = down;
        }
    }
}

归并排序

自底向上合并有序数组
使用辅助数组，使用指针使原数组和辅助数组身份多次交换，最后将结果放回原数组
稳定，合并有序数组时不改变相对位置

public static void MergeSort<T>(IList<T> list)
    where T : IComparable<T>
{
    int count = list.Count;
    IList<T> a = list;
    IList<T> b = new T[count];
    for (int seg = 1; seg < count; seg <<= 1)
    {
        for (int low = 0; low < count; low += seg << 1)
        {
            int mid = Math.Min(count, low + seg);
            int high = Math.Min(count, low + (seg << 1));
            int i = low, j = mid, k = low;
            while (i != mid && j != high)
                b[k++] = a[j].CompareTo(a[i]) < 0 ? a[j++] : a[i++];
            while (i != mid)
                b[k++] = a[i++];
            while (j != high)
                b[k++] = a[j++];
        }
        var swap = a;
        a = b;
        b = swap;
    }
    if (!ReferenceEquals(a, list))
        for (int i = 0; i != count; i++)
            list[i] = a[i];
}
public static void MergeSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    int count = list.Count;
    IList<T> a = list;
    IList<T> b = new T[count];
    for (int seg = 1; seg < count; seg <<= 1)
    {
        for (int low = 0; low < count; low += seg << 1)
        {
            int mid = Math.Min(count, low + seg);
            int high = Math.Min(count, low + (seg << 1));
            int i = low, j = mid, k = low;
            while (i != mid && j != high)
                b[k++] = comp(a[j], a[i]) ? a[j++] : a[i++];
            while (i != mid)
                b[k++] = a[i++];
            while (j != high)
                b[k++] = a[j++];
        }
        var swap = a;
        a = b;
        b = swap;
    }
    if (!ReferenceEquals(a, list))
        for (int i = 0; i != count; i++)
            list[i] = a[i];
}

快速排序

自顶向下使用基准分割数组
使用随机数选择基准（可选）
使用双指针分别从前往后和从后往前（可使用其他方式）
不稳定，双指针的交换会改变顺序

public static void QuickSort<T>(IList<T> list)
    where T : IComparable<T>
{
    Stack<(int, int)> ranges = new Stack<(int, int)>();
    Random rand = new Random();
    ranges.Push((0, list.Count));
    while (ranges.Count != 0)
    {
        (int low, int high) = ranges.Pop();
        if (high <= low + 1)
            continue;
        int temp = rand.Next(low, high);
        T sep = list[temp];
        list[temp] = list[low];
        list[low] = sep;
        int i = low, j = high;
        for (; ; )
        {
            do
                i++;
            while (i < high && list[i].CompareTo(sep) < 0);
            do
                j--;
            while (sep.CompareTo(list[j]) < 0);
            if (i > j)
                break;
            T swap = list[i];
            list[i] = list[j];
            list[j] = swap;
        }
        list[low] = list[j];
        list[j] = sep;
        ranges.Push((low, j));
        ranges.Push((i, high));
    }
}
public static void QuickSort<T>(IList<T> list, Func<T, T, bool> comp)
{
    Stack<(int, int)> ranges = new Stack<(int, int)>();
    Random rand = new Random();
    ranges.Push((0, list.Count));
    while (ranges.Count != 0)
    {
        (int low, int high) = ranges.Pop();
        if (high - low <= 1)
            continue;
        int temp = rand.Next(low, high);
        T sep = list[temp];
        list[temp] = list[low];
        list[low] = sep;
        int i = low, j = high;
        for (; ; )
        {
            do
                i++;
            while (i < high && comp(list[i], sep));
            do
                j--;
            while (comp(sep, list[j]));
            if (i > j)
                break;
            T swap = list[i];
            list[i] = list[j];
            list[j] = swap;
        }
        list[low] = list[j];
        list[j] = sep;
        ranges.Push((low, j));
        ranges.Push((i, high));
    }
}

posted @ 2022-10-27 11:51 Violeshnv 阅读(34) 评论(0) 编辑收藏举报

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C# 实现排序算法

C#实现各种排序

冒泡排序

选择排序

插入排序

希尔排序

堆排序

归并排序

快速排序