【算法】用c#实现自定义字符串编码及围栏解码方法

编写一个函数/方法，它接受2个参数、一个字符串和轨道数，并返回ENCODED字符串。

编写第二个函数/方法，它接受2个参数、一个编码字符串和轨道数，并返回DECODED字符串。

然后使用围栏密码对其进行解码。

这种密码用于通过将每个字符沿着一组“竖状轨道”依次放在对角线上来对字符串进行编码。首先开始对角向下移动。当你到达底部时，反转方向，对角向上移动，直到你到达顶部轨道。继续，直到到达字符串的末尾。然后从左到右读取每个“尾号”以导出编码字符串。

例如，字符串“WEAREDISCOVEREDFLEATONCE”可以在三轨系统中表示如下：
W E C R L T E

E R D S O E E F E A O C

A I V D E N

编码的字符串将是：
WECRLTEERDSOEEFEAOCAIVDEN

对于编码和解码，假设尾号的数量>=2，并且传递空字符串将返回空字符串。

请注意，为了简单起见，上面的示例排除了标点符号和空格。然而，也有一些测试包括标点符号。不要过滤掉标点符号，因为它们是字符串的一部分。

---

算法实现：

 1 using System;
 2 using System.Linq;
 3
 4 public class RailFenceCipher
 5 {
 6    public static string Encode(string s, int n)
 7    {
 8        var mod = (n - 1) * 2;
 9        return string.Concat(s.Select((c, i) => new { c, i })
10           .OrderBy(a => Math.Min(a.i % mod, mod - a.i % mod))
11           .Select(a => a.c));
12    }
13
14    public static string Decode(string s, int n)
15    {
16        var mod = (n - 1) * 2;
17        var pattern = Enumerable.Range(0, s.Length)
18           .OrderBy(i => Math.Min(i % mod, mod - i % mod));
19        return string.Concat(s.Zip(pattern, (c, i) => new { c, i })
20           .OrderBy(a => a.i).Select(a => a.c));
21    }
22 }

测试用例：

  1 using NUnit.Framework;
  2 using System;
  3 using System.Collections.Generic;
  4 using System.Linq;
  5 public class SolutionTest
  6 {
  7     [Test]
  8     public void BasicTests()
  9     {
 10         string[][] config =
 11         {
 12             new[] { "Hello, World!", "Hoo!el,Wrdl l" },               // encode
 13             new[] { "Hello, World!", "Hlo ol!el,Wrd" },               // encode
 14             new[] { "Hello, World!", "H !e,Wdloollr" },               // encode
 15             new[] { "H !e,Wdloollr", "Hello, World!" },               //  decode
 16             new[] { "", "" },                            // encode
 17             new[] { "", "" },                            //  decode
 18             new[] { "WEAREDISCOVEREDFLEEATONCE", "WECRLTEERDSOEEFEAOCAIVDEN" },   // encode
 19             new[] { "WECRLTEERDSOEEFEAOCAIVDEN", "WEAREDISCOVEREDFLEEATONCE" },   //  decode
 20             new[] { "WEAREDISCOVEREDFLEEATONCE", "WIREEEDSEEEACAECVDLTNROFO" },   // encode
 21             new[] { "WIREEEDSEEEACAECVDLTNROFO", "WEAREDISCOVEREDFLEEATONCE" },   //  decode
 22             new[] { "WEAREDISCOVEREDFLEEATONCE", "WCLEESOFECAIVDENRDEEAOERT" },   // encode
 23             new[] { "WECRLTEERDSOEEFEAOCAIVDEN", "WLSADOOTEEECEAEECRFINVEDR" }    //  decode
 24         };
 25         int[] rails = { 3, 2, 4, 4, 3, 3, 3, 3, 4, 4, 5, 5 };
 26         for (int i = 0; i < config.Length; i++)
 27         {
 28             var actual = i % 2 == 0 || i == 1
 29                 ? RailFenceCipher.Encode(config[i][0], rails[i])
 30                 : RailFenceCipher.Decode(config[i][0], rails[i]);
 31
 32             Assert.AreEqual(config[i][1], actual);
 33         }
 34     }
 35
 36     /* *****************
 37      *   RANDOM TESTS
 38      * *****************/
 39
 40     private class Sol
 41     {
 42         private static IEnumerable<T> Fencer<T>(int n, IEnumerable<T> str)
 43         {
 44             var rails = Enumerable.Range(0, n).Select(r => new List<T>()).ToList();
 45             int[] data = { 0, 1 };
 46             int x = 0, dx = 1;
 47             foreach (var t in str)
 48             {
 49                 rails[data[x]].Add(t);
 50                 if (data[x] == n - 1 && data[dx] > 0 || data[x] == 0 && data[dx] < 0)
 51                     data[dx] *= -1;
 52                 data[x] += data[dx];
 53             }
 54             return rails.SelectMany(lst => lst);
 55         }
 56
 57         public static string Encode(string s, int n) => new string(Fencer(n, s).ToArray());
 58
 59         public static string Decode(string s, int n)
 60         {
 61             char[] arr = new char[s.Length];
 62             int[] j = { 0 };
 63             Fencer(n, Enumerable.Range(0, s.Length)).ToList().ForEach(i => arr[i] = s[j[0]++]);
 64             return new string(arr);
 65         }
 66     }
 67
 68     private Random rnd = new Random();
 69
 70     private int Rand(int start, int end) { return start + rnd.Next(end - start); }
 71
 72     [Test]
 73     public void FixedStringVariousRails()
 74     {
 75         var msg = "WEAREDISCOVEREDFLEEATONCE";
 76         Console.WriteLine($"Input for these tests:\n{msg}");
 77
 78         for (int r = 0; r < 10; r++)
 79         {
 80             var rails = Rand(2, 11);
 81             var exp = Sol.Encode(msg, rails);
 82             Assert.AreEqual(exp, RailFenceCipher.Encode(msg, rails));
 83
 84             rails = Rand(2, 11);
 85             exp = Sol.Decode(msg, rails);
 86             Assert.AreEqual(exp, RailFenceCipher.Decode(msg, rails));
 87         }
 88     }
 89
 90     private static string lorem = "Amet non facere minima iure unde, provident, "
 91                                   + "veritatis officiis asperiores ipsa eveniet sit! Deserunt "
 92                                   + "autem excepturi quibusdam iure unde! Porro alias distinctio "
 93                                   + "ipsam iure exercitationem molestiae. Voluptate fugiat quasi maiores!jk";
 94     private static List<string> lorarr = lorem.Split(' ').ToList();
 95
 96     [Test]
 97     public void RandomTests()
 98     {
 99         Console.WriteLine($"Base string for these tests (or a shuffled version):\n{lorem}");
100
101         for (int r = 0; r < 50; r++)
102         {
103             var msg = Shuffle();
104             int rails = Rand(2, 51);
105             var exp = Sol.Encode(msg, rails);
106             Assert.AreEqual(exp, RailFenceCipher.Encode(msg, rails));
107
108             msg = Shuffle();
109             rails = Rand(2, 51);
110             exp = Sol.Decode(msg, rails);
111             Assert.AreEqual(exp, RailFenceCipher.Decode(msg, rails));
112         }
113     }
114
115     private string Shuffle()
116     {
117         Shuffle(lorarr);
118         return string.Join(" ", lorarr);
119     }
120
121     public static void Shuffle<T>(List<T> deck)
122     {
123         var rnd = new Random();
124         for (int n = deck.Count - 1; n > 0; --n)
125         {
126             int k = rnd.Next(n + 1);
127             T temp = deck[n];
128             deck[n] = deck[k];
129             deck[k] = temp;
130         }
131     }
132 }