медленное решение для 10. Regular Expression Matching

10. Regular Expression Matching/10. Regular Expression Matching.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>_10._Regular_Expression_Matching</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

10. Regular Expression Matching/Program.cs

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+var solution = new Solution();
+
+var examples = new (string s, string p, bool expected)[]
+{
+	("aa", "a", false),
+	("aa", "a*", true),
+	("ab", ".*", true),
+	("aab", "c*a*b", true),
+	("mississippi", "mis*is*p*.", false),
+	("mississippi", "mis*is*ip*.", true),
+	("aaa", "a*a", true),
+	("aaa", "ab*a*c*a", true),
+	("ab", ".*c", false),
+	("", "c*", true),
+	("abcd", "d*", false),
+	("", "", true),
+	("a", ".", true),
+	("", "a*", true),
+    ("aa", "b*a*", true),
+    ("a", "ab*", true),
+    ("abcaaaaaaabaabcabac", ".*ab.a.*a*a*.*b*b*", true),
+    ("", "a*b*", true),
+};
+
+foreach (var example in examples)
+{
+	var result = solution.IsMatch(example.s, example.p);
+	Console.WriteLine($"s = \"{example.s}\", p = \"{example.p}\" => {result} (expected {example.expected})");
+}

10. Regular Expression Matching/Solution.cs

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+public class Solution
+{
+    public bool IsMatch(string s, string p) => IsMatch(null, s, p);
+
+    private bool IsMatch(char? prev, ReadOnlySpan<char> str, ReadOnlySpan<char> pattern)
+    {
+        if (pattern.Length == 0 && str.Length == 0)
+            return true;
+        if (str.Length == 0)
+        {
+            if (CanBeEmpty(pattern))
+                return true;
+            return false;
+        }
+        if (pattern.Length == 0)
+            return false;
+        var sym = str[0];
+        var p = pattern[0];
+        // раскрытая звёздочка
+        var pSymOrDot = p == '*' ? prev : p; // превращаем звёздочку в символ или точку
+        // ожидаемый текущий символ, конкретный
+        var pSym = pSymOrDot == '.' ? sym : pSymOrDot;
+
+
+        // следующий символ *
+        if (pattern.Length > 1 && pattern[1] == '*')
+        {
+            var match = false;
+            var i = 0;
+            do
+            {
+                match |= IsMatch(i > 0 ? p : prev, str[i..], pattern[2..]);
+                if (match || i == str.Length || str[i] != p && p != '.')
+                    break;
+                i++;
+            }
+            while (i <= str.Length);
+            return match;
+        }
+        else if (sym != pSym)
+        {
+            return false;
+        }
+        else
+        {
+            return IsMatch(pSymOrDot, str[1..], pattern[1..]);
+        }
+    }
+
+    private bool CanBeEmpty(ReadOnlySpan<char> pattern)
+    {
+        if (pattern.Length % 2 == 1)
+            return false;
+        for (var i = 1; i < pattern.Length; i += 2)
+            if (pattern[i] != '*')
+                return false;
+        return true;
+    }
+}