字母递增

 1 　　　　 /// <summary>
 2         /// 过滤，取最大值
 3         /// </summary>
 4         /// <returns>Id</returns>
 5         public string FilteringId()
 6         {
 7             // 英字4桁のIdからMAX値取得
 8             var regex = new Regex(@"^[a-z]{4}$");
 9             string[] idList = this.XXRepo.All().Select(m => m.Id).ToArray();
10             string maxId = idList.Where(m => regex.IsMatch(m) && m != "zzzz").Max();
11             if (string.Empty.Equals(maxId))
12             {
13                 return "aaaa";
14             }
15             return this.NumberingForId(maxId);
16         }
17 //------------------------------cut-line---------------------------------------------------------
18 　　　　 /// <summary>
19         /// 进位
20         /// </summary>
21         /// <param name="maxId">maxId</param>
22         /// <returns>Id</returns>
23         public string NumberingForId(string maxId)
24         {
25             int length = maxId.Length;
26             char[] ch = new char[length];
27             for (int i = 0; i < length; i++)
28             {
29                 ch[i] = maxId[i];
30             }
31             // 进位
32             bool carry = true;
33             int p = length;
34             while (carry)
35             {
36                 p--;
37                 ch[p] = this.LetterIncrement(ch[p]);
38                 if (ch[p] == 'a')
39                 {
40                     carry = true;
41                 }
42                 else
43                 {
44                     carry = false;
45                 }
46             }
47             return new string(ch);
48         }
49 //-------------------cut-line-------------------------------------------------
50 　　　　 /// <summary>
51         /// 进位方法
52         /// </summary>
53         /// <param name="ch">ch</param>
54         /// <returns>ch</returns>
55         public char LetterIncrement(char ch)
56         {
57             if (ch == 122)
58             {
59                 ch = (char)97;
60             }
61             else
62             {
63                 ch++;
64             }
65             return ch;
66         }
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