Add Wildcard Pattern Matching (#470)

Algorithms.Tests/Strings/PatternMatching/WildCardMatcherTests.cs

@@ -0,0 +1,36 @@
+using Algorithms.Strings.PatternMatching;
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Strings.PatternMatching;
+
+public static class WildCardMatcherTests
+{
+    [TestCase("aab", "c*a*b", true)]
+    [TestCase("aaa", "aa", false)]
+    [TestCase("aaa", "a.a", true)]
+    [TestCase("aaab", "aa*", false)]
+    [TestCase("aaab", ".*", true)]
+    [TestCase("a", "bbbb", false)]
+    [TestCase("", "bbbb", false)]
+    [TestCase("a", "", false)]
+    [TestCase("", "", true)]
+    public static void MatchPattern(string inputString, string pattern, bool expected)
+    {
+        // Act
+        var result = WildCardMatcher.MatchPattern(inputString, pattern);
+
+        // Assert
+        Assert.That(result, Is.EqualTo(expected));
+    }
+
+    [Test]
+    public static void MatchPatternThrowsArgumentException()
+    {
+        // Arrange
+        var inputString = "abc";
+        var pattern = "*abc";
+
+        // Assert
+        Assert.Throws<System.ArgumentException>(() => WildCardMatcher.MatchPattern(inputString, pattern));
+    }
+}

Algorithms/Strings/PatternMatching/WildCardMatcher.cs

@@ -0,0 +1,97 @@
+using System;
+
+namespace Algorithms.Strings.PatternMatching;
+
+/// <summary>
+///     Implentation of regular expression matching with support for '.' and '*'.
+///     '.' Matches any single character.
+///     '*' Matches zero or more of the preceding element.
+///     The matching should cover the entire input string (not partial).
+/// </summary>
+public static class WildCardMatcher
+{
+    /// <summary>
+    ///    Using bottom-up dynamic programming for matching the input string with the pattern.
+    ///
+    ///    Time complexity: O(n*m), where n is the length of the input string and m is the length of the pattern.
+    ///
+    ///    Constrain: The pattern cannot start with '*'.
+    /// </summary>
+    /// <param name="inputString">The input string to match.</param>
+    /// <param name="pattern">The pattern to match.</param>
+    /// <returns>True if the input string matches the pattern, false otherwise.</returns>
+    /// <exception cref="ArgumentException">Thrown when the pattern starts with '*'.</exception>
+    public static bool MatchPattern(string inputString, string pattern)
+    {
+        if (pattern.Length > 0 && pattern[0] == '*')
+        {
+            throw new ArgumentException("Pattern cannot start with *");
+        }
+
+        var inputLength = inputString.Length + 1;
+        var patternLength = pattern.Length + 1;
+
+        // DP 2d matrix, where dp[i, j] is true if the first i characters in the input string match the first j characters in the pattern
+        // This DP is initialized to all falses, as it is the default value for a boolean.
+        var dp = new bool[inputLength, patternLength];
+
+        // Empty string and empty pattern are a match
+        dp[0, 0] = true;
+
+        // Since the empty string can only match a pattern that has a * in it, we need to initialize the first row of the DP matrix
+        for (var j = 1; j < patternLength; j++)
+        {
+            if (pattern[j - 1] == '*')
+            {
+                dp[0, j] = dp[0, j - 2];
+            }
+        }
+
+        // Now using bottom-up approach to find for all remaining lenghts of input and pattern
+        for (var i = 1; i < inputLength; i++)
+        {
+            for (var j = 1; j < patternLength; j++)
+            {
+                MatchRemainingLenghts(inputString, pattern, dp, i, j);
+            }
+        }
+
+        return dp[inputLength - 1, patternLength - 1];
+    }
+
+    // Helper method to match the remaining lengths of the input string and the pattern
+    // This method is called for all i and j where i > 0 and j > 0
+    private static void MatchRemainingLenghts(string inputString, string pattern, bool[,] dp, int i, int j)
+    {
+        // If the characters match or the pattern has a ., then the result is the same as the previous positions.
+        if (inputString[i - 1] == pattern[j - 1] || pattern[j - 1] == '.')
+        {
+            dp[i, j] = dp[i - 1, j - 1];
+        }
+        else if (pattern[j - 1] == '*')
+        {
+            MatchForZeroOrMore(inputString, pattern, dp, i, j);
+        }
+        else
+        {
+            // If the characters do not match, then the result is false, which is the default value.
+        }
+    }
+
+    // Helper method to match for the "*" pattern.
+    private static void MatchForZeroOrMore(string inputString, string pattern, bool[,] dp, int i, int j)
+    {
+        if (dp[i, j - 2])
+        {
+            dp[i, j] = true;
+        }
+        else if (inputString[i - 1] == pattern[j - 2] || pattern[j - 2] == '.')
+        {
+            dp[i, j] = dp[i - 1, j];
+        }
+        else
+        {
+            // Leave the default value of false
+        }
+    }
+}

README.md

@@ -191,6 +191,7 @@ find more than one implementation for the same objective but using different alg
       * [Rabin Karp](./Algorithms/Strings/PatternMatching/RabinKarp.cs)
       * [Boyer Moore](./Algorithms/Strings/PatternMatching/BoyerMoore.cs)
       * [Knuth–Morris–Pratt Search](./Algorithms/Strings/PatternMatching/KnuthMorrisPrattSearcher.cs)
+      * [WildCard Pattern Matching](./Algorithms/Strings/PatternMatching/WildCardMatcher.cs)
       * [Z-block substring search](./Algorithms/Strings/PatternMatching/ZblockSubstringSearch.cs)
     * [Longest Consecutive Character](./Algorithms/Strings/GeneralStringAlgorithms.cs)
     * [Palindrome Checker](./Algorithms/Strings/Palindrome.cs)