Add Knuth-Morris-Pratt algorithm

build.gradle

@@ -5,7 +5,7 @@ plugins {
 repositories {
     mavenLocal()
     maven {
-        url = 'http://repo.maven.apache.org/maven2'
+        url = 'https://repo.maven.apache.org/maven2'
     }
 }
 

src/main/java/com/others/KMP.java

@@ -0,0 +1,62 @@
+package com.others;
+import java.util.ArrayList;
+
+/**
+ * Implementation of the Knuth–Morris–Pratt algorithm
+ */
+public class KMP {
+
+    /**
+     * KMPmatcher method finds if any string "needle" is in the string "haystack" and returns the index of its first letter for all occurrencies.
+     * @param haystack string in which the method is searching
+     * @param needle string which the method is searching for
+     * @return an ArrayList of starting indexes of the haystack that matches the searched needle
+     */
+    public static ArrayList<Integer> KMPmatcher(final String haystack, final String needle) {
+        final int haystackLength = haystack.length();
+        final int needleLength = needle.length();
+        final int[] pi = computePrefixFunction(needle);
+        int matchingLength = 0;
+        ArrayList<Integer> startingIndexes = new ArrayList<>();
+        for (int i = 0; i < haystackLength; i++) {
+            while (matchingLength > 0 && haystack.charAt(i) != needle.charAt(matchingLength)) {
+                matchingLength = pi[matchingLength - 1];
+            }
+
+            if (haystack.charAt(i) == needle.charAt(matchingLength)) {
+                matchingLength++;
+            }
+
+            if (matchingLength == needleLength) {
+                startingIndexes.add(i + 1 - needleLength);
+                matchingLength = pi[matchingLength - 1];
+            }
+        }
+        return startingIndexes;
+    }
+
+    /**
+     * The computePrefixFunction method gets the prefix function of the given string.
+     * @param P string (this should be the needle in the KNP)
+     * @return an array of indexes of the given sting where it matches itself
+     */
+    private static int[] computePrefixFunction(final String P) {
+        final int stringLength = P.length();
+        final int[] pi = new int[stringLength];
+        pi[0] = 0;
+        int matchingLength = 0;
+        for (int i = 1; i < stringLength; i++) {
+            while (matchingLength > 0 && P.charAt(i) != P.charAt(matchingLength)) {
+                matchingLength = pi[matchingLength - 1];
+            }
+
+            if (P.charAt(i) == P.charAt(matchingLength)) {
+                matchingLength++;
+            }
+
+            pi[i] = matchingLength;
+
+        }
+        return pi;
+    }
+}

src/test/java/com/others/KMPTest.java

@@ -0,0 +1,22 @@
+package com.others;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+
+class KMPTest {
+
+    @Test
+    void testKMP() {
+        KMP kmp = new KMP();
+
+        ArrayList<Integer> result = new ArrayList<>();
+        result.add(0);
+        result.add(1);
+        Assertions.assertEquals(result, kmp.KMPmatcher("AAAAABAAABA", "AAAA"), "Incorrect Conversion");
+
+        ArrayList<Integer> result2 = new ArrayList<>();
+        Assertions.assertEquals(result2, kmp.KMPmatcher("ABABABA", "AAAA"), "Incorrect Conversion");
+    }
+}