C# 快速排序--二分查找法--拉格朗日插值法

1.快速排序

 参考自: https://www.cnblogs.com/yundan/p/4022056.html

namespace 快速排序算法
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("请输入待排序数列以 , 分割");
            string _s = Console.ReadLine();
            string[] _sArray = _s.Split(",".ToCharArray());
            int _nLength = _sArray.Length;
            int[] _nArray = new int[_nLength];
            for (int i = 0; i < _nLength; i++)
            {
                _nArray[i] = Convert.ToInt32(_sArray[i]);
            }

            var list = _nArray.ToList();
            QuickSort(list, 0, _nLength - 1);

            foreach (var i in list)
            {
                Console.WriteLine(i.ToString());
            }
            Console.ReadLine();
        }
 
        //left为0,right为数组长度减一,即分别为数组中第一个和最后一个数的索引
        private static int Division(List<int> list, int left, int right)   
        {
            while (left < right)
            {
                int num = list[left]; //将首元素作为分割位置
                if (num > list[left + 1]) //前一位 > 后一位
                {
                    list[left] = list[left + 1];  //将两处位置对调
                    list[left + 1] = num;
                    left++;
                }
                else
                {
                    int temp = list[right];
                    list[right] = list[left + 1];
                    list[left + 1] = temp;
                    right--;
                }
                Console.WriteLine(string.Join(",", list));
            }
            Console.WriteLine("--------------\n");
            return left; //指向的此时枢轴的位置
        }
        private static void QuickSort(List<int> list, int left, int right)
        {
            if (left < right)
            {
                int i = Division(list, left, right);
                //对枢轴的左边部分进行排序
                QuickSort(list,  i + 1, right);
                //对枢轴的右边部分进行排序
                QuickSort(list, left, i - 1);
            }
        }
    }
}

2.二分查找法

namespace 二分查找法
{   
    class Program
    {
      // 数组,low=0,high为数组长度减一,key为查找的数字
        public static int BinarySearch(int[]arr,int low,int high,int key)
        {
            int mid = (low + high) / 2; //中间数字
            if (low > high)
            {
                return -1;     //查找不到
            }
            else
            {
                if (arr[mid] == key)
                {
                    return mid;
                }
                else if (arr[mid] > key)
                {
                    return BinarySearch(arr, low, mid - 1, key);
                }
                else
                {
                    return BinarySearch(arr, mid + 1, high, key);
                }
            }
        }
        static void Main(string[] args)
        {
            int[] shuzu = { 1, 2, 5, 6, 8,12,16,17,17,19,21,26,28,29,34 }; //先排好大小顺序
            int high = shuzu.Length - 1;
            int jieguo = BinarySearch(shuzu, 0, high, 16);
            Console.WriteLine("查找数字下标:"+jieguo);
            Console.WriteLine("数组长度:"+shuzu.Length );
            Console.ReadLine();
        }
    }
}

输出:

 

3.拉格朗日插值法

namespace 拉格朗日插值法
{
    class Program
    {
        private static int Cha(int[] shuzhu, int key)
        {
            int left = 0;  //数组中起始位置下标
            int right = shuzhu.Length - 1; //数组最后一位下标
            int middle = -1;//查找不到
            while (left <= right)
            {
                middle = left + (right - left) * (key - shuzhu[left]) / (shuzhu[right] - shuzhu[left]);
                if (key == shuzhu[middle])
                {
                    return middle;
                }
                else if (key > shuzhu[middle])
                {
                    left = middle + 1;
                }
                else
                {
                    right = middle - 1;
                }
            }
            return -1;
        }
        static void Main(string[] args)
        {
            int[] num = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ,45,46,48};
            int a = Cha(num, 4);//查找数组中数值为4的下标
            Console.WriteLine(a);
            Console.ReadLine();
        }
    }
}

输出: