shyamlibakale1001-alt · Nov 11, 2026
diff --git a/src/main/java/com/thealgorithms/ciphers/Autokey.java b/src/main/java/com/thealgorithms/ciphers/Autokey.java
@@ -11,7 +11,22 @@
  */
 public class Autokey {
 
-    // Encrypts the plaintext using the Autokey cipher
+    /**
+     * Encrypts the plaintext using the Autokey cipher.
+     *
+     * <p>Protected conditions:
+     * <ul>
+     * <li>Normalizes {@code plaintext} to uppercase and strips non-letter characters
+     * ({@code [^A-Z]}) before indexing, and uppercases {@code keyword}.</li>
+     * <li>Appends the sanitized {@code plaintext} to {@code keyword} to form the autokey stream,
+     * covering all {@code 0 <= i < plaintext.length()} characters.</li>
+     * <li>Wraps character sums modulo 26 over {@code 'A'..'Z'}.</li>
+     * </ul>
+     *
+     * @param plaintext input message to encrypt
+     * @param keyword   initial cipher keyword
+     * @return uppercase ciphertext over {@code 'A'..'Z'}
+     */
     public String encrypt(String plaintext, String keyword) {
         plaintext = plaintext.toUpperCase().replaceAll("[^A-Z]", ""); // Sanitize input
         keyword = keyword.toUpperCase();

diff --git a/src/test/java/com/thealgorithms/ciphers/AutokeyTest.java b/src/test/java/com/thealgorithms/ciphers/AutokeyTest.java
@@ -33,4 +33,66 @@ void autokeyDecryptTest() {
         // then
         assertEquals("MEETATDAWN", plainText);
     }
+
+    private static void logCase(String id, String input, String expected, String actual) {
+        System.out.println("[R45-T020] " + id + " | input=" + input
+            + " | expected=" + expected + " | actual=" + actual);
+    }
+
+    /**
+     * Mutation-resistant regression for {@link Autokey#encrypt(String, String)}.
+     *
+     * <p>Source preconditions ({@code Autokey.java}):
+     * <ul>
+     * <li>lines 31-32: uppercases {@code plaintext} and strips {@code [^A-Z]} (line 31);
+     * uppercases {@code keyword} (line 32)</li>
+     * <li>lines 34-35: {@code extendedKey = keyword + sanitizedPlaintext}</li>
+     * <li>line 39: loop runs for {@code 0 <= i < plaintext.length()}</li>
+     * <li>line 43: {@code (plainChar - 'A' + keyChar - 'A') % 26 + 'A'} wraps modulo 26</li>
+     * </ul>
+     */
+    @Test
+    void encryptSmallestOrdinaryAndBoundaryInputsDetectMutants() {
+        // Smallest valid inputs: empty after sanitization (line 31 & line 39) and 1-char minimal
+        String emptyActual = autokeyCipher.encrypt("", "A");
+        logCase("smallest-empty", "(\"\", \"A\")", "", emptyActual);
+        assertEquals("", emptyActual);
+
+        String strippedEmptyActual = autokeyCipher.encrypt("123!", "A");
+        logCase("smallest-nonalpha", "(\"123!\", \"A\")", "", strippedEmptyActual);
+        assertEquals("", strippedEmptyActual);
+
+        // Minimal 1-char plaintext protects loop bound `i < plaintext.length()` (line 39)
+        String minCharActual = autokeyCipher.encrypt("A", "B");
+        logCase("smallest-one-char", "(\"A\", \"B\")", "B", minCharActual);
+        assertEquals("B", minCharActual);
+
+        // Wrap-around boundary: ('Z' - 'A' + 'B' - 'A') % 26 + 'A' = 26 % 26 + 'A' = 'A' (line 43)
+        String wrapActual = autokeyCipher.encrypt("Z", "B");
+        logCase("boundary-mod-26-wrap", "(\"Z\", \"B\")", "A", wrapActual);
+        assertEquals("A", wrapActual);
+
+        // Minimal autokey extension: keyword "D" (len 1) + plaintext "BC" -> extendedKey "DBC" (line 35)
+        // i=0: B(1)+D(3)=E(4); i=1: C(2)+B(1)=D(3)
+        String autokeyActual = autokeyCipher.encrypt("BC", "D");
+        logCase("boundary-autokey-extension", "(\"BC\", \"D\")", "ED", autokeyActual);
+        assertEquals("ED", autokeyActual);
+
+        // Ordinary input with lowercase, spaces, and 12-char plaintext > 5-char keyword:
+        // "attack at dawn" -> "ATTACKATDAWN", key "queen" -> "QUEENATTACKATDAWN" -> "QNXEPKTMDCGN"
+        String origPlain = "attack at dawn";
+        String origKey = "queen";
+        String ordinaryActual = autokeyCipher.encrypt(origPlain, origKey);
+        logCase("ordinary-lowercase-spaced", "(\"attack at dawn\", \"queen\")",
+            "QNXEPKTMDCGN", ordinaryActual);
+        assertEquals("QNXEPKTMDCGN", ordinaryActual);
+        assertEquals(12, ordinaryActual.length());
+
+        // Fresh equivalent sanitized call produces identical output; inputs remain unmutated
+        String freshEquivalent = autokeyCipher.encrypt("ATTACKATDAWN", "QUEEN");
+        assertEquals("QNXEPKTMDCGN", freshEquivalent);
+        assertEquals("attack at dawn", origPlain);
+        assertEquals("queen", origKey);
+        assertEquals("ATTACKATDAWN", autokeyCipher.decrypt(ordinaryActual, origKey));
+    }
 }
diff --git a/work/R45-T020/check.py b/work/R45-T020/check.py
@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Runner for task R45-T020: mutation-resistant checks for Autokey.encrypt.
+
+Runs the focused JUnit test through Maven, requires a nonzero test count,
+saves inputs, expected versus actual results, and tool versions into work/R45-T020/,
+and exits non-zero on any failure.
+"""
+import glob
+import subprocess
+import sys
+import xml.etree.ElementTree as ET
+from pathlib import Path
+
+HERE = Path(__file__).resolve().parent
+REPO = HERE.parent.parent
+TEST_CLASS = "AutokeyCipherTest"
+CMD = ["mvn", "-B", "test", f"-Dtest={TEST_CLASS}", "-Dsurefire.failIfNoSpecifiedTests=false"]
+
+
+def tool_version(cmd):
+    try:
+        out = subprocess.run(cmd, capture_output=True, text=True, cwd=REPO)
+        return "\n".join(l for l in (out.stdout + out.stderr).splitlines()
+                         if not l.startswith("Picked up")).strip()
+    except FileNotFoundError:
+        return f"{cmd[0]}: not found"
+
+
+def main():
+    (HERE / "tool_versions.txt").write_text(
+        "java:\n" + tool_version(["java", "-version"]) + "\n\nmvn:\n"
+        + tool_version(["mvn", "-v"]) + "\n\npython:\n" + sys.version + "\n")
+
+    print("Running:", " ".join(CMD))
+    proc = subprocess.run(CMD, capture_output=True, text=True, cwd=REPO)
+    combined_output = proc.stdout + proc.stderr
+    (HERE / "mvn_output.txt").write_text(combined_output)
+
+    records = [line.strip() for line in combined_output.splitlines()
+               if line.strip().startswith("[R45-T020]")]
+    (HERE / "comparisons.txt").write_text(
+        ("\n".join(records) + "\n") if records else "No regression records captured.\n")
+
+    reports = glob.glob(str(REPO / "target/surefire-reports" / f"TEST-*{TEST_CLASS}.xml"))
+    if not reports:
+        (HERE / "result.txt").write_text(
+            f"command: {' '.join(CMD)}\nFAIL: no surefire report found\n")
+        print("FAIL: no surefire report found")
+        return 1
+
+    suite = ET.parse(reports[0]).getroot()
+    tests = int(suite.get("tests", 0))
+    failures = int(suite.get("failures", 0)) + int(suite.get("errors", 0))
+    skipped = int(suite.get("skipped", 0))
+    passed = proc.returncode == 0 and failures == 0 and tests > 0 and len(records) > 0
+    status = "PASS" if passed else "FAIL"
+    summary = (
+        f"command: {' '.join(CMD)}\n"
+        f"tests={tests} failures/errors={failures} skipped={skipped} "
+        f"records={len(records)} mvn_exit={proc.returncode}\n"
+        f"status={status}\n"
+    )
+    (HERE / "result.txt").write_text(summary)
+    print(summary)
+
+    return 0 if passed else 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/work/R45-T020/comparisons.txt b/work/R45-T020/comparisons.txt
@@ -0,0 +1,6 @@
+[R45-T020] smallest-empty | input=("", "A") | expected= | actual=
+[R45-T020] smallest-nonalpha | input=("123!", "A") | expected= | actual=
+[R45-T020] smallest-one-char | input=("A", "B") | expected=B | actual=B
+[R45-T020] boundary-mod-26-wrap | input=("Z", "B") | expected=A | actual=A
+[R45-T020] boundary-autokey-extension | input=("BC", "D") | expected=ED | actual=ED
+[R45-T020] ordinary-lowercase-spaced | input=("attack at dawn", "queen") | expected=QNXEPKTMDCGN | actual=QNXEPKTMDCGN
diff --git a/work/R45-T020/mvn_output.txt b/work/R45-T020/mvn_output.txt
@@ -0,0 +1,55 @@
+[INFO] Scanning for projects...
+[INFO] Loaded 24447 auto-discovered prefixes for remote repository central (prefixes-central.txt)
+[INFO] 
+[INFO] -----------------------< com.thealgorithms:Java >-----------------------
+[INFO] Building Java 1.0-SNAPSHOT
+[INFO]   from pom.xml
+[INFO] --------------------------------[ jar ]---------------------------------
+[INFO] 
+[INFO] --- jacoco:0.8.16:prepare-agent (default) @ Java ---
+[INFO] Loaded 64 auto-discovered prefixes for remote repository apache.snapshots (prefixes-apache.snapshots.txt)
+[INFO] argLine set to -javaagent:/Users/shyamlibakale/.m2/repository/org/jacoco/org.jacoco.agent/0.8.16/org.jacoco.agent-0.8.16-runtime.jar=destfile=/Users/shyamlibakale/TheAlgorithms-Java/TheAlgorithms-Java/target/jacoco.exec
+[INFO] 
+[INFO] --- resources:3.5.0:resources (default-resources) @ Java ---
+[INFO] skip non existing resourceDirectory /Users/shyamlibakale/TheAlgorithms-Java/TheAlgorithms-Java/src/main/resources
+[INFO] 
+[INFO] --- compiler:3.16.0:compile (default-compile) @ Java ---
+[INFO] Recompiling the module because of changed source code.
+[INFO] Compiling 848 source files with javac [debug release 21] to target/classes
+[INFO] 
+[INFO] --- resources:3.5.0:testResources (default-testResources) @ Java ---
+[INFO] skip non existing resourceDirectory /Users/shyamlibakale/TheAlgorithms-Java/TheAlgorithms-Java/src/test/resources
+[INFO] 
+[INFO] --- compiler:3.16.0:testCompile (default-testCompile) @ Java ---
+[INFO] Recompiling the module because of changed dependency.
+[INFO] Compiling 796 source files with javac [debug release 21] to target/test-classes
+[INFO] 
+[INFO] --- surefire:3.6.0:test (default-test) @ Java ---
+[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
+[INFO] 
+[INFO] -------------------------------------------------------
+[INFO]  T E S T S
+[INFO] -------------------------------------------------------
+[INFO] Running com.thealgorithms.ciphers.AutokeyCipherTest
+[R45-T020] smallest-empty | input=("", "A") | expected= | actual=
+[R45-T020] smallest-nonalpha | input=("123!", "A") | expected= | actual=
+[R45-T020] smallest-one-char | input=("A", "B") | expected=B | actual=B
+[R45-T020] boundary-mod-26-wrap | input=("Z", "B") | expected=A | actual=A
+[R45-T020] boundary-autokey-extension | input=("BC", "D") | expected=ED | actual=ED
+[R45-T020] ordinary-lowercase-spaced | input=("attack at dawn", "queen") | expected=QNXEPKTMDCGN | actual=QNXEPKTMDCGN
+[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.045 s -- in com.thealgorithms.ciphers.AutokeyCipherTest
+[INFO] 
+[INFO] Results:
+[INFO] 
+[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0
+[INFO] 
+[INFO] 
+[INFO] --- jacoco:0.8.16:report (generate-code-coverage-report) @ Java ---
+[INFO] Loading execution data file /Users/shyamlibakale/TheAlgorithms-Java/TheAlgorithms-Java/target/jacoco.exec
+[INFO] Analyzed bundle 'Java' with 1073 classes
+[INFO] ------------------------------------------------------------------------
+[INFO] BUILD SUCCESS
+[INFO] ------------------------------------------------------------------------
+[INFO] Total time:  5.787 s
+[INFO] Finished at: 2026-11-11T20:29:56+05:30
+[INFO] ------------------------------------------------------------------------
diff --git a/work/R45-T020/result.txt b/work/R45-T020/result.txt
@@ -0,0 +1,3 @@
+command: mvn -B test -Dtest=AutokeyCipherTest -Dsurefire.failIfNoSpecifiedTests=false
+tests=3 failures/errors=0 skipped=0 records=6 mvn_exit=0
+status=PASS
diff --git a/work/R45-T020/tool_versions.txt b/work/R45-T020/tool_versions.txt
@@ -0,0 +1,14 @@
+java:
+openjdk version "21.0.13" 2026-10-20 LTS
+OpenJDK Runtime Environment Temurin-21.0.13+9 (build 21.0.13+9-LTS)
+OpenJDK 64-Bit Server VM Temurin-21.0.13+9 (build 21.0.13+9-LTS, mixed mode, sharing)
+
+mvn:
+Apache Maven 3.10.0 (c43a36b8d67be7e0805a411bc0898af1a51f5472)
+Maven home: /opt/homebrew/Cellar/maven/3.10.0/libexec
+Java version: 27.0.1.0.3, vendor: Homebrew, runtime: /opt/homebrew/Cellar/openjdk/27.0.1.0.3/libexec/openjdk.jdk/Contents/Home
+Default locale: en_IN, platform encoding: UTF-8, time zone: Asia/Kolkata
+OS name: "mac os x", version: "27.0", arch: "aarch64", family: "mac"
+
+python:
+3.14.7 (v3.14.7:823f0323ee6, Aug  5 2026, 07:07:01) [Clang 21.0.0 (clang-2100.1.1.101)]