From 622241ed3e034baf5cf52228e75ae1cb2dfc96c1 Mon Sep 17 00:00:00 2001
From: "utkarshishu2627@gmail.com" <utkarshishu2627@gmail.com>
Date: Wed, 26 Nov 2025 07:12:36 +0530
Subject: [PATCH 1/5] Add Z-Algorithm (string pattern matching) with tests

---
 DIRECTORY.md                                  |  2 ++
 .../com/thealgorithms/strings/ZAlgorithm.java | 29 +++++++++++++++++++
 .../thealgorithms/strings/ZAlgorithmTest.java | 23 +++++++++++++++
 3 files changed, 54 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/strings/ZAlgorithm.java
 create mode 100644 src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 042efa72addc..c278b6915d49 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -821,6 +821,7 @@
           - 📄 [Upper](src/main/java/com/thealgorithms/strings/Upper.java)
           - 📄 [ValidParentheses](src/main/java/com/thealgorithms/strings/ValidParentheses.java)
           - 📄 [WordLadder](src/main/java/com/thealgorithms/strings/WordLadder.java)
+          - 📄 [ZAlgorithm](src/main/java/com/thealgorithms/strings/ZAlgorithm.java)
           - 📁 **zigZagPattern**
             - 📄 [ZigZagPattern](src/main/java/com/thealgorithms/strings/zigZagPattern/ZigZagPattern.java)
         - 📁 **tree**
@@ -1578,6 +1579,7 @@
           - 📄 [UpperTest](src/test/java/com/thealgorithms/strings/UpperTest.java)
           - 📄 [ValidParenthesesTest](src/test/java/com/thealgorithms/strings/ValidParenthesesTest.java)
           - 📄 [WordLadderTest](src/test/java/com/thealgorithms/strings/WordLadderTest.java)
+          - 📄 [ZAlgorithmTest](src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java)
           - 📁 **zigZagPattern**
             - 📄 [ZigZagPatternTest](src/test/java/com/thealgorithms/strings/zigZagPattern/ZigZagPatternTest.java)
         - 📁 **tree**
diff --git a/src/main/java/com/thealgorithms/strings/ZAlgorithm.java b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
new file mode 100644
index 000000000000..951f31ddd19d
--- /dev/null
+++ b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
@@ -0,0 +1,29 @@
+package com.thealgorithms.strings;
+
+public class ZAlgorithm {
+
+    public static int[] zFunction(String s) {
+        int n = s.length();
+        int[] z = new int[n];
+        int l = 0, r = 0;
+        for (int i = 1; i < n; i++) {
+            if (i <= r) z[i] = Math.min(r - i + 1, z[i - l]);
+            while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i])) z[i]++;
+            if (i + z[i] - 1 > r) {
+                l = i;
+                r = i + z[i] - 1;
+            }
+        }
+        return z;
+    }
+
+    public static int search(String text, String pattern) {
+        String s = pattern + "$" + text;
+        int[] z = zFunction(s);
+        int p = pattern.length();
+        for (int i = 0; i < z.length; i++) {
+            if (z[i] == p) return i - p - 1;
+        }
+        return -1;
+    }
+}
diff --git a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
new file mode 100644
index 000000000000..6cd0eeb3c901
--- /dev/null
+++ b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
@@ -0,0 +1,23 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+public class ZAlgorithmTest {
+
+    @Test
+    void testZFunction() {
+        int[] z = ZAlgorithm.zFunction("aaaaa");
+        assertArrayEquals(new int[]{0, 4, 3, 2, 1}, z);
+    }
+
+    @Test
+    void testSearchFound() {
+        assertEquals(2, ZAlgorithm.search("abcabca", "cab"));
+    }
+
+    @Test
+    void testSearchNotFound() {
+        assertEquals(-1, ZAlgorithm.search("abcdef", "gh"));
+    }
+}

From 7d21bea7f0fdc7aab529fee7e01e0e752b92d77d Mon Sep 17 00:00:00 2001
From: "utkarshishu2627@gmail.com" <utkarshishu2627@gmail.com>
Date: Wed, 26 Nov 2025 07:26:07 +0530
Subject: [PATCH 2/5] Add Z-Algorithm (string pattern matching) with tests

---
 src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
index 6cd0eeb3c901..d1aa5f077ec1 100644
--- a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
+++ b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
@@ -1,3 +1,6 @@
+/*
+ * https://en.wikipedia.org/wiki/Z-algorithm
+ */
 package com.thealgorithms.strings;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -8,7 +11,7 @@ public class ZAlgorithmTest {
     @Test
     void testZFunction() {
         int[] z = ZAlgorithm.zFunction("aaaaa");
-        assertArrayEquals(new int[]{0, 4, 3, 2, 1}, z);
+        assertArrayEquals(new int[] { 0, 4, 3, 2, 1 }, z);
     }
 
     @Test

From 935d9e8944a01bb2e6d878f78707285dbe7f03cd Mon Sep 17 00:00:00 2001
From: "utkarshishu2627@gmail.com" <utkarshishu2627@gmail.com>
Date: Wed, 26 Nov 2025 07:27:07 +0530
Subject: [PATCH 3/5] Add Z-Algorithm (string pattern matching) with tests

---
 .../java/com/thealgorithms/strings/ZAlgorithm.java  | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/main/java/com/thealgorithms/strings/ZAlgorithm.java b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
index 951f31ddd19d..81d1ae70cd6a 100644
--- a/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
+++ b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
@@ -1,3 +1,7 @@
+/*
+ * https://en.wikipedia.org/wiki/Z-algorithm
+ */
+
 package com.thealgorithms.strings;
 
 public class ZAlgorithm {
@@ -7,8 +11,10 @@ public static int[] zFunction(String s) {
         int[] z = new int[n];
         int l = 0, r = 0;
         for (int i = 1; i < n; i++) {
-            if (i <= r) z[i] = Math.min(r - i + 1, z[i - l]);
-            while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i])) z[i]++;
+            if (i <= r)
+                z[i] = Math.min(r - i + 1, z[i - l]);
+            while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i]))
+                z[i]++;
             if (i + z[i] - 1 > r) {
                 l = i;
                 r = i + z[i] - 1;
@@ -22,7 +28,8 @@ public static int search(String text, String pattern) {
         int[] z = zFunction(s);
         int p = pattern.length();
         for (int i = 0; i < z.length; i++) {
-            if (z[i] == p) return i - p - 1;
+            if (z[i] == p)
+                return i - p - 1;
         }
         return -1;
     }

From 8e58ef67efa3b0b4e511974d3a72a0686b88aa7f Mon Sep 17 00:00:00 2001
From: "utkarshishu2627@gmail.com" <utkarshishu2627@gmail.com>
Date: Wed, 26 Nov 2025 07:34:53 +0530
Subject: [PATCH 4/5] Fix checkstyle errors for ZAlgorithm

---
 .../com/thealgorithms/strings/ZAlgorithm.java | 24 ++++++++++++++-----
 .../thealgorithms/strings/ZAlgorithmTest.java |  7 +++---
 2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/src/main/java/com/thealgorithms/strings/ZAlgorithm.java b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
index 81d1ae70cd6a..dc029b751f45 100644
--- a/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
+++ b/src/main/java/com/thealgorithms/strings/ZAlgorithm.java
@@ -1,25 +1,35 @@
 /*
  * https://en.wikipedia.org/wiki/Z-algorithm
  */
-
 package com.thealgorithms.strings;
 
-public class ZAlgorithm {
+public final class ZAlgorithm {
+
+    private ZAlgorithm() {
+        throw new UnsupportedOperationException("Utility class");
+    }
 
     public static int[] zFunction(String s) {
         int n = s.length();
         int[] z = new int[n];
-        int l = 0, r = 0;
+        int l = 0;
+        int r = 0;
+
         for (int i = 1; i < n; i++) {
-            if (i <= r)
+            if (i <= r) {
                 z[i] = Math.min(r - i + 1, z[i - l]);
-            while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i]))
+            }
+
+            while (i + z[i] < n && s.charAt(z[i]) == s.charAt(i + z[i])) {
                 z[i]++;
+            }
+
             if (i + z[i] - 1 > r) {
                 l = i;
                 r = i + z[i] - 1;
             }
         }
+
         return z;
     }
 
@@ -27,9 +37,11 @@ public static int search(String text, String pattern) {
         String s = pattern + "$" + text;
         int[] z = zFunction(s);
         int p = pattern.length();
+
         for (int i = 0; i < z.length; i++) {
-            if (z[i] == p)
+            if (z[i] == p) {
                 return i - p - 1;
+            }
         }
         return -1;
     }
diff --git a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
index d1aa5f077ec1..d7e5ae027d28 100644
--- a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
+++ b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
@@ -1,9 +1,8 @@
-/*
- * https://en.wikipedia.org/wiki/Z-algorithm
- */
 package com.thealgorithms.strings;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import org.junit.jupiter.api.Test;
 
 public class ZAlgorithmTest {

From 4e0c78beda8d2c5fcf083bb4c9eeb7cc3ac5abc3 Mon Sep 17 00:00:00 2001
From: "utkarshishu2627@gmail.com" <utkarshishu2627@gmail.com>
Date: Wed, 26 Nov 2025 08:15:29 +0530
Subject: [PATCH 5/5] Fix: clang-format and checkstyle compliance for
 ZAlgorithm

---
 src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
index d7e5ae027d28..df749ed9a8b5 100644
--- a/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
+++ b/src/test/java/com/thealgorithms/strings/ZAlgorithmTest.java
@@ -10,7 +10,7 @@ public class ZAlgorithmTest {
     @Test
     void testZFunction() {
         int[] z = ZAlgorithm.zFunction("aaaaa");
-        assertArrayEquals(new int[] { 0, 4, 3, 2, 1 }, z);
+        assertArrayEquals(new int[] {0, 4, 3, 2, 1}, z);
     }
 
     @Test