算法系列15天速成 第四天 五大经典查找【上】

namespace Sequential
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int>() { 2, 3, 5, 8, 7 };

            var result = SequenceSearch(list, 3);

            if (result != -1)
                Console.WriteLine("3 已经在数组中找到，索引位置为：" + result);
            else
                Console.WriteLine("呜呜，没有找到！");

            Console.Read();
        }

        //顺序查找
        static int SequenceSearch(List<int> list, int key)
        {
            for (int i = 0; i < list.Count; i++)
            {
                //查找成功，返回序列号
                if (key == list[i])
                    return i;
            }
            //未能查找，返回-1
            return -1;
        }
    }
}

namespace BinarySearch
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int>() { 3, 7, 9, 10, 11, 24, 45, 66, 77 };

            var result = BinarySearch(list, 45);

            if (result != -1)
                Console.WriteLine("45 已经在数组中找到，索引位置为：" + result);
            else
                Console.WriteLine("呜呜，没有找到！");

            Console.Read();
        }

        ///<summary>
/// 折半查找
///</summary>
///<param name="list"></param>
///<returns></returns>
        public static int BinarySearch(List<int> list, int key)
        {
            //最低线
            int low = 0;

            //最高线
            int high = list.Count - 1;

            while (low <= high)
            {
                //取中间值
                var middle = (low + high) / 2;

                if (list[middle] == key)
                {
                    return middle;
                }
                else
                    if (list[middle] > key)
                    {
                        //下降一半
                        high = middle - 1;
                    }
                    else
                    {
                        //上升一半
                        low = middle + 1;
                    }
            }
            //未找到
            return -1;
        }
    }
}