Add zAlgorithm

Author: harry0000

src/main/scala/io/github/acl4s/String.scala

@@ -0,0 +1,34 @@
+package io.github.acl4s
+
+import scala.reflect.ClassTag
+
+/**
+ * Reference:
+ * D. Gusfield,
+ * Algorithms on Strings, Trees, and Sequences: Computer Science and
+ * Computational Biology
+ */
+private[acl4s] def zAlgorithmImpl[T: ClassTag](s: Array[T]): Array[Int] = {
+  val n = s.length
+  if (n == 0) {
+    return Array.empty
+  }
+  val z = new Array[Int](n)
+  z(0) = 0
+  var j = 0
+  for (i <- 1 until n) {
+    var k = if (j + z(j) <= i) { 0 }
+    else { Math.min(j + z(j) - i, z(i - j)) }
+    while (i + k < n && s(k) == s(i + k)) {
+      k += 1
+    }
+    z(i) = k
+    if (j + z(j) < i + z(i)) {
+      j = i
+    }
+  }
+  z(0) = n
+  z
+}
+
+def zAlgorithm(s: String): Array[Int] = zAlgorithmImpl(s.toCharArray)

src/test/scala/io/github/acl4s/StringSuite.scala

@@ -0,0 +1,20 @@
+package io.github.acl4s
+
+class StringSuite extends munit.FunSuite {
+
+  test("zAlgorithm") {
+    {
+      val str = "abracadabra";
+      val lcp = zAlgorithm(str)
+
+      assertEquals(lcp.toSeq, Seq(11, 0, 0, 1, 0, 1, 0, 4, 0, 0, 1))
+    }
+    {
+      val str = "ababababa"
+      val lcp = zAlgorithm(str)
+
+      assertEquals(lcp.toSeq, Seq(9, 0, 7, 0, 5, 0, 3, 0, 1))
+    }
+  }
+
+}