Short chain generation and chain generation

Short chain generation and chain generation

1 /// <summary> 2 // short chain generation 3 /// </summary> 4 public class ShortUrlBuilder 5 {6 private static readonly string [] Chars = 7 {" ", "B", "c", "d", "e", "f", "g", "h", 8 9 "I", "j ", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t ", 10 11 "u", "v", "w", "x", "y", "z", "0", "1", "2 ", "3", "4", "5", 12 13 "6", "7", "8", "9", "A", "B ", "C", "D", "E", "F", "G", "H", 14 15 "I", "J", "K", "L", "M", "N", "O", "P", "Q ", "R", "S", "T", 16 17 "U", "V", "W", "X", "Y", "Z" 18 }; 19 20 /// <summary> 21 /// generate the summary of the specified URL 22 /// </summary> 23 // <param name = "url"> URL </ param> 24 // <returns> short chain list, just take one storage. </Returns> 25 public static List <string> Build (string url) 26 {27 var shortUrls = new List <string> (); 28 if (url = null) 29 {30 return shortUrls; 31} 32 var hash = GetMd5 (url); 33 // divide the md5 code of 32 characters into four segments for processing, each segment contains 8 characters 34 for (int I = 0; I <4; I ++) 35 {36 37 int offset = I * 8; 38 39 string sub = hash. substring (offset, 8); 40 41 long sub16 = long. parse (sub, NumberStyles. hexNumber); // convert sub into a hexadecimal number to long42 43 // & 0X 3 FFFFFFF: remove the first two digits, leaving only 30 digits 44 sub16 & = 0X3FFFFFFF; 45 46 StringBuilder sb = new StringBuilder (); 47 // divide the remaining 30 digits into 6 segments, each segment with 5 digits 48 for (int j = 0; j <6; j ++) 49 {50 // get a <= 61 digit 51 long t = sub16 & 0x0000003D; 52 sb. append (Chars [(int) t]); 53 54 sub16> = 5; // shifts sub16 right to 5 digits 55} 56 57 shortUrls. add (sb. toString (); 58} 59 return shortUrls; 60} 61 62 // <summary> 63 // MD5 encryption 64 // </summary> 65 // <param name = "myString"> Original string </param> 66 // <param name = "salt"> salt </param> 67 // <returns> </returns> 68 private static string GetMd5 (string myString, string salt = "") 69 {70 if (myString! = Null) 71 {72 var array = myString. toCharArray (); 73 Array. reverse (array); 74 myString = $ "{new string (array)} + {{{ salt }}}"; 75 76 # if DEBUG77 Debugger. log (1, "2", $ "custom message: {myString} \ r \ n"); 78 # endif79 MD5 = MD5.Create (); 80 byte [] bs = Encoding. UTF8.GetBytes (myString); 81 byte [] hs = md5.ComputeHash (bs); 82 StringBuilder sb = new StringBuilder (); 83 foreach (byte B in hs) 84 {85 // format 86 sb in hexadecimal format. append (B. toString ("x2"); 87} 88 return sb. toString (); 89 90} 91 return null; 92} 93}