【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
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, rails)
30 : RailFenceCipher.Decode(config, rails);
31
32 Assert.AreEqual(config, 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].Add(t);
50 if (data == n - 1 && data > 0 || data == 0 && data < 0)
51 data *= -1;
52 data += data;
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;
62 int[] j = { 0 };
63 Fencer(n, Enumerable.Range(0, s.Length)).ToList().ForEach(i => arr = s++]);
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
73 public void FixedStringVariousRails()
74 {
75 var msg = "WEAREDISCOVEREDFLEEATONCE";
76 Console.WriteLine($"Input for these tests:\n{msg}");
77
78 for (int r = 0; r < 10; r++)
79 {
80 var rails = Rand(2, 11);
81 var exp = Sol.Encode(msg, rails);
82 Assert.AreEqual(exp, RailFenceCipher.Encode(msg, rails));
83
84 rails = Rand(2, 11);
85 exp = Sol.Decode(msg, rails);
86 Assert.AreEqual(exp, RailFenceCipher.Decode(msg, rails));
87 }
88 }
89
90 private static string lorem = "Amet non facere minima iure unde, provident, "
91 + "veritatis officiis asperiores ipsa eveniet sit! Deserunt "
92 + "autem excepturi quibusdam iure unde! Porro alias distinctio "
93 + "ipsam iure exercitationem molestiae. Voluptate fugiat quasi maiores!jk";
94 private static List<string> lorarr = lorem.Split(' ').ToList();
95
96
97 public void RandomTests()
98 {
99 Console.WriteLine($"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;
128 deck = deck;
129 deck = temp;
130 }
131 }
132 }
来源:https://www.cnblogs.com/lan80/archive/2023/08/21/17645151.html
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