获取指定数量的有序列表
信息系统中经常用到排序、查找等简单的数据结构，结合大数据量的后台设计实践；
将插入排序、折半查找结合起来，实现一个经常用的场景：实时从海量数据中获取指定数量产品的有序列表
1 /// <summary> 2 /// 插入排序 3 /// 获取前count个有序列表 4 /// </summary> 5 /// <param name="list"></param> 6 /// <param name="count"></param> 7 /// <returns></returns> 8 public static List<decimal> GetSortCountList(List<decimal> list, int count = int.MaxValue) 9 { 10 var result = new List<decimal>(); 11 foreach (var item in list) 12 { 13 int index = GetOrderByIndex(result, item, count); 14 if (index > -1) 15 { 16 result.Insert(index, item); 17 if (result.Count > count) 18 { 19 result.RemoveAt(count); 20 } 21 } 22 } 23 return result; 24 } 25 26 /// <summary> 27 /// 插入排序 28 /// 返回数值应该插入的index 29 /// </summary> 30 /// <param name="list"></param> 31 /// <param name="price"></param> 32 /// <returns></returns> 33 public static int GetOrderByIndex(List<decimal> list, decimal price, int count = int.MaxValue) 34 { 35 int length = list.Count; 36 if (length == 0) 37 { 38 return 0; 39 } 40 else 41 { 42 if (price >= list.Last())//大于等于最大 43 { 44 return length < count ? length : -1; 45 } 46 else if (price <= list.First()) //小于等于最小 47 { 48 return 0; 49 } 50 else//最小-->最大之间 51 { 52 return GetOrderByIndex(list, price, 1, length - 1); 53 } 54 } 55 } 56 57 /// <summary> 58 /// 折半查找 59 /// 返回数值应该插入的index 60 /// </summary> 61 /// <param name="list"></param> 62 /// <param name="item"></param> 63 /// <param name="first"></param> 64 /// <param name="last"></param> 65 /// <returns></returns> 66 public static int GetOrderByIndex(List<decimal> list, decimal item, int first, int last) 67 { 68 int middle = (last + first) / 2; 69 var middlePrice = list[middle]; 70 if (last <= first) 71 { 72 return (item < middlePrice) ? middle : middle + 1; 73 } 74 else 75 { 76 if (item < middlePrice) 77 { 78 return GetOrderByIndex(list, item, first, middle - 1); 79 } 80 else 81 { 82 return GetOrderByIndex(list, item, middle + 1, last); 83 } 84 } 85 }
