【愚公系列】2023年11月 七大查找算法(七)-分块查找

namespace IndexSearch.CSharp
{
    /// <summary>
    /// 索引项实体
    /// </summary>
    public class IndexItem
    {
        public int Index { get; set; } 

        public int Start { get; set; }

        public int Length { get; set; }

    }

    public class Program
    {
        /// <summary>
        /// 主表
        /// </summary>
        static int[] studentList = new int[] {
            101,102,103,104,105,0,0,0,0,0,
            201,202,203,204,0,0,0,0,0,0,
            301,302,303,0,0,0,0,0,0,0
        };

        /// <summary>
        /// 索引表
        /// </summary>
        static IndexItem[] IndexItemList = new IndexItem[] {
            new IndexItem{ Index=1,Start=0,Length=5},
            new IndexItem{ Index=2,Start=10,Length=4},
            new IndexItem{ Index=3,Start=20,Length=3}
        };

        /// <summary>
        /// 索引查找算法
        /// </summary>
        /// <param name="key">给定值</param>
        /// <returns>给定值在表中的位置</returns>
        public static int IndexSearch(int key)
        {
            IndexItem item = null;

            // 建立索引规则
            var index = key / 100;

            //遍历索引表,找到对应的索引项
            for (int i = 0; i < IndexItemList.Count(); i++)
            {
                //找到索引项
                if (IndexItemList[i].Index == index)
                {
                    item = new IndexItem() { Start = IndexItemList[i].Start, Length = IndexItemList[i].Length };
                    break;
                }
            }

            //索引表中不存在该索引项
            if (item == null)
                return -1;

            //在主表顺序查找
            for (int i = item.Start; i < item.Start + item.Length; i++)
            {
                if (studentList[i] == key)
                {
                    return i;
                }
            }
            return -1;
        }

        /// <summary>
        /// 插入数据
        /// </summary>
        /// <param name="key"></param>
        /// <returns>true,插入成功，false,插入失败</returns>
        public static bool Insert(int key)
        {
            IndexItem item = null;

            try
            {
                //建立索引规则
                var index = key / 100;

                int i = 0;

                //遍历索引表,找到对应的索引项
                for (i = 0; i < IndexItemList.Count(); i++)
                {
                    if (IndexItemList[i].Index == index)
                    {
                        item = new IndexItem()
                        {
                            Start = IndexItemList[i].Start,
                            Length = IndexItemList[i].Length
                        };
                        break;
                    }
                }

                //索引表中不存在该索引项
                if (item == null)
                    return false;

                //依索引项将值插入到主表中
                studentList[item.Start + item.Length] = key;

                //更新索引表
                IndexItemList[i].Length++;
            }
            catch
            {
                return false;
            }
            return true;
        }

        static void Main(string[] args)
        {
            Console.WriteLine("********************索引查找(C#版)********************\n");
            Console.WriteLine("原始数据：{0}",String.Join(" ",studentList));

            int value = 205;
            Console.WriteLine("插入数据:{0}",value);
            //插入成功
            if (Insert(value))
            {
                Console.WriteLine("\n插入后数据:{0}",String.Join(",", studentList));
                Console.WriteLine("\n元素205在列表中的位置为:{0} ",IndexSearch(value));
            }

            Console.ReadKey();
        }
    }
}