Add BoyerMoore activity

Author: jcazevedo

src/main/java/com/packt/datastructuresandalg/lesson5/activity/boyermoore/BoyerMoore.java

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+package com.packt.datastructuresandalg.lesson5.activity.boyermoore;
+
+import java.util.List;
+
+public class BoyerMoore {
+    public List<Integer> match(String P, String T) { return null; }
+}

src/main/java/com/packt/datastructuresandalg/lesson5/activity/boyermoore/solution/BoyerMoore.java

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+package com.packt.datastructuresandalg.lesson5.activity.boyermoore.solution;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class BoyerMoore {
+    public List<Integer> match(String P, String T) {
+        int n = T.length();
+        int m = P.length();
+
+        int e = 256;
+        int right[][] = new int[m][e];
+        for (int i = 0; i < m; i++)
+            for (int j = 0; j < e; j++)
+                right[i][j] = -1;
+        for (int i = 0; i < m; i++) {
+            if (i != 0)
+                for (int j = 0; j < e; j++)
+                    right[i][j] = right[i - 1][j];
+            right[i][P.charAt(i)] = i;
+        }
+
+        int i = m, j = m + 1;
+        int[] f = new int[m + 1];
+        int[] s = new int[m + 1];
+        f[i] = j;
+        while (i > 0) {
+            while (j <= m && P.charAt(i - 1) != P.charAt(j - 1)) {
+                if (s[j] == 0)
+                    s[j] = j - i;
+                j = f[j];
+            }
+            i--; j--;
+            f[i] = j;
+        }
+
+        j = f[0];
+        for (i = 0; i <= m; i++) {
+            if (s[i] == 0)
+                s[i] = j;
+            if (i == j)
+                j = f[j];
+        }
+
+        List<Integer> shifts = new ArrayList<>();
+        int skip;
+        for (i = 0; i < n - m + 1; i += skip) {
+            skip = 0;
+            boolean hasMatch = true;
+            for (j = m - 1; j >= 0; j--) {
+                if (P.charAt(j) != T.charAt(i + j)) {
+                    hasMatch = false;
+                    skip = Math.max(s[j + 1], j - right[j][T.charAt(i + j)]);
+                    break;
+                }
+            }
+            if (hasMatch) {
+                shifts.add(i);
+                skip = s[0];
+            }
+        }
+        return shifts;
+    }
+
+    public static void main(String[] args) {
+        BoyerMoore bm = new BoyerMoore();
+        List<Integer> matches = bm.match("rabrabracad", "abacadabrabracabracadabrabrabracad");
+        for (Integer i : matches)
+            System.out.println(i);
+    }
+}

src/test/java/com/packt/datastructuresandalg/lesson5/activity/boyermoore/BoyerMooreTest.java

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+package com.packt.datastructuresandalg.lesson5.activity.boyermoore;
+
+import junit.framework.TestCase;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+public class BoyerMooreTest extends TestCase {
+    BoyerMoore bm = new BoyerMoore();
+
+    public void test1() {
+        assertTrue(bm.match("abc", "abc").equals(Arrays.asList(0)));
+    }
+
+    public void test2() {
+        assertTrue(bm.match("abd", "abc").equals(new ArrayList<>()));
+    }
+
+    public void test3() {
+        assertTrue(bm.match("abcde", "abc").equals(new ArrayList<>()));
+    }
+
+    public void test4() {
+        assertTrue(bm.match("aab", "acaabc").equals(Arrays.asList(2)));
+    }
+
+    public void test5() {
+        assertTrue(bm.match("aab", "acaabcaab").equals(Arrays.asList(2, 6)));
+    }
+
+    public void test6() {
+        assertTrue(bm.match("rabrabracad", "abacadabrabracabracadabrabrabracad").equals(Arrays.asList(23)));
+    }
+
+}