排序算法-归并排序

自底向下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _010_归并排序
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] data = new int[] { 42, 20, 17, 27, 13, 8, 17, 48, 65 };
          
            mergeSort(data, 0, data.Length - 1);
            for (int i = 0; i < data.Length; i++)
            {
                Console.Write(data[i] + " ");
            }
        }

        public static void mergearray(int[] arrayData,int low,int mid,int high)
        {
             int[] aux = new int[high - low + 1];
            int i = low;//左指针
            int j = mid + 1;//右指针
            int k = 0;//临时数组指针
            //把较小的数先移动新数组中
            while (i<=mid && j<=high)
            {
                if (arrayData[i] <= arrayData[j])
                {
                    aux[k++] = arrayData[i++];
                }
                else
                {
                    aux[k++] = arrayData[j++];
                }
            }
            //把左边剩余的数移入数组
            while (i<=mid)
            {
                aux[k++] = arrayData[i++];
            }
            //把右边边剩余的数移入数组
            while (j <= high)
            {
                aux[k++] = arrayData[j++];
            }
            // 把新数组中的数覆盖原数组
            for (int t = 0; t < aux.Length; t++)
            {
                arrayData[t+low] = aux[t];
            }
        }
        /// <summary>
        /// 自顶向下的归并排序
        /// </summary>
        /// <param name="arrayData"></param>
        /// <param name="low"></param>
        /// <param name="high"></param>
        public static void mergeSort(int[] arrayData,int low,int high)
        {
           
            if (low < high)
            {
                int mid = low + (high - low) / 2;
                //左边
                mergeSort(arrayData, low, mid);
                //右边
                mergeSort(arrayData, mid+1,high);
                //左右并归
                mergearray(arrayData, low, mid, high);
            }
        }

自底向上：

 /// <summary>
        /// 自底向上的归并排序
        /// </summary>
        /// <param name="arrayData"></param>
        /// <param name="low"></param>
        /// <param name="high"></param>
        public static void mergeSort_2(int[] arrayData, int low, int high)
        {
            int N = arrayData.Length;
            for (int i = 1; i < N;i=i+i)//增量的数组
            {
                for (int j = 0; j < N-i; j+=i+i)//每个增量比较的次数
                {
                    mergearray(arrayData,j,j+i-1,Math.Min(j+i+i-1,N-1));
                }
            }
        }