Refactor KMP and RabinKarp: Improve Reusability and Test Coverage (#7250)

* first commit

* Running KMPTest and RabinKarpTest with fixed formatting

* now build failed error resolved

* now build failed error resolved 2

---------

Co-authored-by: Divyansh Saxena <divyanshsaxena@gmail.com>
Co-authored-by: Deniz Altunkapan <deniz.altunkapan@outlook.com>

src/test/java/com/thealgorithms/strings/KMPTest.java

@@ -0,0 +1,29 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+public class KMPTest {
+
+    @Test
+    public void testNullInputs() {
+        assertEquals(List.of(), KMP.kmpMatcher(null, "A"));
+        assertEquals(List.of(), KMP.kmpMatcher("A", null));
+        assertEquals(List.of(), KMP.kmpMatcher(null, null));
+    }
+
+    @Test
+    public void testKMPMatcher() {
+        assertEquals(List.of(0, 1), KMP.kmpMatcher("AAAAABAAABA", "AAAA"));
+        assertEquals(List.of(0, 3), KMP.kmpMatcher("ABCABC", "ABC"));
+        assertEquals(List.of(10), KMP.kmpMatcher("ABABDABACDABABCABAB", "ABABCABAB"));
+        assertEquals(List.of(), KMP.kmpMatcher("ABCDE", "FGH"));
+        assertEquals(List.of(), KMP.kmpMatcher("A", "AA"));
+        assertEquals(List.of(0, 1, 2), KMP.kmpMatcher("AAA", "A"));
+        assertEquals(List.of(0), KMP.kmpMatcher("A", "A"));
+        assertEquals(List.of(), KMP.kmpMatcher("", "A"));
+        assertEquals(List.of(), KMP.kmpMatcher("A", ""));
+    }
+}

src/test/java/com/thealgorithms/strings/RabinKarpTest.java

@@ -0,0 +1,46 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+public class RabinKarpTest {
+
+    @Test
+    public void testNullInputs() {
+        assertEquals(List.of(), RabinKarp.search(null, "A"));
+        assertEquals(List.of(), RabinKarp.search("A", null));
+        assertEquals(List.of(), RabinKarp.search(null, null));
+    }
+
+    @Test
+    public void testHashCollision() {
+        // 'a' = 97. (char)198 % 101 = 97.
+        // For length 1, h = 1. p = 97. t = 198 % 101 = 97.
+        // Collision occurs, loop checks characters: 198 != 97, breaks.
+        char collisionChar = (char) 198;
+        String text = String.valueOf(collisionChar);
+        String pattern = "a";
+        assertEquals(List.of(), RabinKarp.search(text, pattern));
+    }
+
+    @Test
+    public void testSearchWithCustomQ() {
+        // Using a different prime
+        assertEquals(List.of(0, 1), RabinKarp.search("AAAA", "AAA", 13));
+    }
+
+    @Test
+    public void testRabinKarpSearch() {
+        assertEquals(List.of(0, 1), RabinKarp.search("AAAAABAAABA", "AAAA"));
+        assertEquals(List.of(0, 3), RabinKarp.search("ABCABC", "ABC"));
+        assertEquals(List.of(10), RabinKarp.search("ABABDABACDABABCABAB", "ABABCABAB"));
+        assertEquals(List.of(), RabinKarp.search("ABCDE", "FGH"));
+        assertEquals(List.of(), RabinKarp.search("A", "AA"));
+        assertEquals(List.of(0, 1, 2), RabinKarp.search("AAA", "A"));
+        assertEquals(List.of(0), RabinKarp.search("A", "A"));
+        assertEquals(List.of(), RabinKarp.search("", "A"));
+        assertEquals(List.of(), RabinKarp.search("A", ""));
+    }
+}