shyamlibakale1001-alt · Nov 11, 2026
diff --git a/src/main/java/com/thealgorithms/others/Mandelbrot.java b/src/main/java/com/thealgorithms/others/Mandelbrot.java
@@ -91,9 +91,8 @@ public static BufferedImage getImage(int imageWidth, int imageHeight, double fig
         // loop through the image-coordinates
         for (int imageX = 0; imageX < imageWidth; imageX++) {
             for (int imageY = 0; imageY < imageHeight; imageY++) {
-                // determine the figure-coordinates based on the image-coordinates
-                double figureX = figureCenterX + ((double) imageX / imageWidth - 0.5) * figureWidth;
-                double figureY = figureCenterY + ((double) imageY / imageHeight - 0.5) * figureHeight;
+                double figureX = pixelToFigureCoordinate(imageX, imageWidth, figureCenterX, figureWidth);
+                double figureY = pixelToFigureCoordinate(imageY, imageHeight, figureCenterY, figureHeight);
 
                 double distance = getDistance(figureX, figureY, maxStep);
 
@@ -105,6 +104,19 @@ public static BufferedImage getImage(int imageWidth, int imageHeight, double fig
         return image;
     }
 
+    /**
+     * Maps a pixel index along one image axis to its corresponding coordinate in figure space.
+     *
+     * @param pixelIndex Zero-based pixel index along the axis.
+     * @param imageSpan Total number of pixels along the axis.
+     * @param figureCenter Figure-space coordinate at the center of the axis.
+     * @param figureSpan Total width (or height) of the figure along the axis.
+     * @return The figure-space coordinate corresponding to {@code pixelIndex}.
+     */
+    private static double pixelToFigureCoordinate(int pixelIndex, int imageSpan, double figureCenter, double figureSpan) {
+        return figureCenter + ((double) pixelIndex / imageSpan - 0.5) * figureSpan;
+    }
+
     /**
      * Black and white color-coding that ignores the relative distance. The
      * Mandelbrot set is black, everything else is white.

diff --git a/src/test/java/com/thealgorithms/others/MandelbrotTest.java b/src/test/java/com/thealgorithms/others/MandelbrotTest.java
@@ -0,0 +1,132 @@
+package com.thealgorithms.others;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.awt.Color;
+import java.awt.image.BufferedImage;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Regression tests for {@link Mandelbrot#getImage(int, int, double, double, double, int, boolean)}.
+ *
+ * <p>Source anchors ({@code Mandelbrot.java}, {@code main} lines 32-47):
+ * <ul>
+ * <li>{@code blackAndWhiteImage = getImage(800, 600, -0.6, 0, 3.2, 50, false)}</li>
+ * <li>{@code blackAndWhiteImage.getRGB(0, 0) == new Color(255, 255, 255).getRGB()} (line 35)</li>
+ * <li>{@code blackAndWhiteImage.getRGB(400, 300) == new Color(0, 0, 0).getRGB()} (line 38)</li>
+ * <li>{@code coloredImage = getImage(800, 600, -0.6, 0, 3.2, 50, true)}</li>
+ * <li>{@code coloredImage.getRGB(0, 0) == new Color(255, 0, 0).getRGB()} (line 44)</li>
+ * <li>{@code coloredImage.getRGB(400, 300) == new Color(0, 0, 0).getRGB()} (line 47)</li>
+ * </ul>
+ */
+public class MandelbrotTest {
+
+    private static void logCase(String id, String input, Object expected, Object actual) {
+        System.out.println("[R45-T016] " + id + " | input=" + input
+            + " | expected=" + expected + " | actual=" + actual);
+    }
+
+    /**
+     * Executable source anchors from {@code Mandelbrot.main} (lines 32-47) plus neighboring pixel
+     * {@code (1, 0)} (figure coordinates {@code (-2.196, -1.2)}, diverging at step 0).
+     */
+    @Test
+    public void sourceAnchorsAndNeighboringPixelMatchExpectedRgb() {
+        BufferedImage bw = Mandelbrot.getImage(800, 600, -0.6, 0, 3.2, 50, false);
+        assertEquals(800, bw.getWidth());
+        assertEquals(600, bw.getHeight());
+        assertEquals(BufferedImage.TYPE_INT_RGB, bw.getType());
+
+        int white = new Color(255, 255, 255).getRGB();
+        int black = new Color(0, 0, 0).getRGB();
+        int red = new Color(255, 0, 0).getRGB();
+
+        int bw00 = bw.getRGB(0, 0);
+        logCase("anchor-bw-0-0", "800x600 bw (0,0)", white, bw00);
+        assertEquals(white, bw00);
+
+        int bw400300 = bw.getRGB(400, 300);
+        logCase("anchor-bw-400-300", "800x600 bw (400,300)", black, bw400300);
+        assertEquals(black, bw400300);
+
+        int bw10 = bw.getRGB(1, 0);
+        logCase("neighbor-bw-1-0", "800x600 bw (1,0)", white, bw10);
+        assertEquals(white, bw10);
+
+        BufferedImage colored = Mandelbrot.getImage(800, 600, -0.6, 0, 3.2, 50, true);
+        int col00 = colored.getRGB(0, 0);
+        logCase("anchor-colored-0-0", "800x600 colored (0,0)", red, col00);
+        assertEquals(red, col00);
+
+        int col400300 = colored.getRGB(400, 300);
+        logCase("anchor-colored-400-300", "800x600 colored (400,300)", black, col400300);
+        assertEquals(black, col400300);
+
+        int col10 = colored.getRGB(1, 0);
+        logCase("neighbor-colored-1-0", "800x600 colored (1,0)", red, col10);
+        assertEquals(red, col10);
+    }
+
+    /**
+     * Independently hand-calculated {@code 2x2} image centered at {@code (0, 0)} with
+     * {@code figureWidth = 2.0, maxStep = 5}:
+     * <ul>
+     * <li>{@code (0, 0)} -> {@code (-1.0, -1.0)} breaks at step 1 -> {@code distance = 0.25} ->
+     * color {@code (127, 255, 0)}</li>
+     * <li>{@code (0, 1)} -> {@code (-1.0, 0.0)} period-2 cycle -> {@code distance = 1.0} ->
+     * black {@code (0, 0, 0)}</li>
+     * <li>{@code (1, 1)} -> {@code (0.0, 0.0)} fixed point -> {@code distance = 1.0} ->
+     * black {@code (0, 0, 0)}</li>
+     * </ul>
+     */
+    @Test
+    public void independentlyCalculatedSmallGridMatchesExactPixelValues() {
+        BufferedImage bw = Mandelbrot.getImage(2, 2, 0.0, 0.0, 2.0, 5, false);
+        BufferedImage colored = Mandelbrot.getImage(2, 2, 0.0, 0.0, 2.0, 5, true);
+
+        int white = new Color(255, 255, 255).getRGB();
+        int black = new Color(0, 0, 0).getRGB();
+        int expectedColor00 = new Color(127, 255, 0).getRGB();
+
+        logCase("grid-2x2-bw-0-0", "2x2 bw (0,0)", white, bw.getRGB(0, 0));
+        assertEquals(white, bw.getRGB(0, 0));
+
+        logCase("grid-2x2-colored-0-0", "2x2 colored (0,0)", expectedColor00, colored.getRGB(0, 0));
+        assertEquals(expectedColor00, colored.getRGB(0, 0));
+
+        logCase("grid-2x2-colored-0-1", "2x2 colored (0,1)", black, colored.getRGB(0, 1));
+        assertEquals(black, colored.getRGB(0, 1));
+
+        logCase("grid-2x2-colored-1-1", "2x2 colored (1,1)", black, colored.getRGB(1, 1));
+        assertEquals(black, colored.getRGB(1, 1));
+    }
+
+    /**
+     * Parameter validation contract (lines 76-86): non-positive dimensions or {@code maxStep}
+     * throw {@link IllegalArgumentException} with specific messages.
+     */
+    @Test
+    public void invalidArgumentsThrowIllegalArgumentException() {
+        IllegalArgumentException badWidth = assertThrows(
+            IllegalArgumentException.class,
+            () -> Mandelbrot.getImage(0, 10, 0, 0, 2.0, 10, false));
+        logCase("invalid-width", "imageWidth=0",
+            "imageWidth should be greater than zero", badWidth.getMessage());
+        assertEquals("imageWidth should be greater than zero", badWidth.getMessage());
+
+        IllegalArgumentException badHeight = assertThrows(
+            IllegalArgumentException.class,
+            () -> Mandelbrot.getImage(10, 0, 0, 0, 2.0, 10, false));
+        logCase("invalid-height", "imageHeight=0",
+            "imageHeight should be greater than zero", badHeight.getMessage());
+        assertEquals("imageHeight should be greater than zero", badHeight.getMessage());
+
+        IllegalArgumentException badStep = assertThrows(
+            IllegalArgumentException.class,
+            () -> Mandelbrot.getImage(10, 10, 0, 0, 2.0, 0, false));
+        logCase("invalid-maxStep", "maxStep=0",
+            "maxStep should be greater than zero", badStep.getMessage());
+        assertEquals("maxStep should be greater than zero", badStep.getMessage());
+    }
+}
diff --git a/work/R45-T016/check.py b/work/R45-T016/check.py
@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+"""Runner for task R45-T016: focused refactoring checks for Mandelbrot.
+
+Runs the focused JUnit test through Maven, requires a nonzero test count,
+saves inputs, expected versus actual results, and tool versions into work/R45-T016/,
+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 = "MandelbrotTest"
+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-T016]")]
+    (HERE / "comparisons.txt").write_text(
+        ("\n".join(records) + "\n") if records else "No check 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-T016/comparisons.txt b/work/R45-T016/comparisons.txt
@@ -0,0 +1,13 @@
+[R45-T016] grid-2x2-bw-0-0 | input=2x2 bw (0,0) | expected=-1 | actual=-1
+[R45-T016] grid-2x2-colored-0-0 | input=2x2 colored (0,0) | expected=-8388864 | actual=-8388864
+[R45-T016] grid-2x2-colored-0-1 | input=2x2 colored (0,1) | expected=-16777216 | actual=-16777216
+[R45-T016] grid-2x2-colored-1-1 | input=2x2 colored (1,1) | expected=-16777216 | actual=-16777216
+[R45-T016] invalid-width | input=imageWidth=0 | expected=imageWidth should be greater than zero | actual=imageWidth should be greater than zero
+[R45-T016] invalid-height | input=imageHeight=0 | expected=imageHeight should be greater than zero | actual=imageHeight should be greater than zero
+[R45-T016] invalid-maxStep | input=maxStep=0 | expected=maxStep should be greater than zero | actual=maxStep should be greater than zero
+[R45-T016] anchor-bw-0-0 | input=800x600 bw (0,0) | expected=-1 | actual=-1
+[R45-T016] anchor-bw-400-300 | input=800x600 bw (400,300) | expected=-16777216 | actual=-16777216
+[R45-T016] neighbor-bw-1-0 | input=800x600 bw (1,0) | expected=-1 | actual=-1
+[R45-T016] anchor-colored-0-0 | input=800x600 colored (0,0) | expected=-65536 | actual=-65536
+[R45-T016] anchor-colored-400-300 | input=800x600 colored (400,300) | expected=-16777216 | actual=-16777216
+[R45-T016] neighbor-colored-1-0 | input=800x600 colored (1,0) | expected=-65536 | actual=-65536
diff --git a/work/R45-T016/mvn_output.txt b/work/R45-T016/mvn_output.txt
@@ -0,0 +1,62 @@
+[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 797 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.others.MandelbrotTest
+[R45-T016] grid-2x2-bw-0-0 | input=2x2 bw (0,0) | expected=-1 | actual=-1
+[R45-T016] grid-2x2-colored-0-0 | input=2x2 colored (0,0) | expected=-8388864 | actual=-8388864
+[R45-T016] grid-2x2-colored-0-1 | input=2x2 colored (0,1) | expected=-16777216 | actual=-16777216
+[R45-T016] grid-2x2-colored-1-1 | input=2x2 colored (1,1) | expected=-16777216 | actual=-16777216
+[R45-T016] invalid-width | input=imageWidth=0 | expected=imageWidth should be greater than zero | actual=imageWidth should be greater than zero
+[R45-T016] invalid-height | input=imageHeight=0 | expected=imageHeight should be greater than zero | actual=imageHeight should be greater than zero
+[R45-T016] invalid-maxStep | input=maxStep=0 | expected=maxStep should be greater than zero | actual=maxStep should be greater than zero
+[R45-T016] anchor-bw-0-0 | input=800x600 bw (0,0) | expected=-1 | actual=-1
+[R45-T016] anchor-bw-400-300 | input=800x600 bw (400,300) | expected=-16777216 | actual=-16777216
+[R45-T016] neighbor-bw-1-0 | input=800x600 bw (1,0) | expected=-1 | actual=-1
+[R45-T016] anchor-colored-0-0 | input=800x600 colored (0,0) | expected=-65536 | actual=-65536
+[R45-T016] anchor-colored-400-300 | input=800x600 colored (400,300) | expected=-16777216 | actual=-16777216
+[R45-T016] neighbor-colored-1-0 | input=800x600 colored (1,0) | expected=-65536 | actual=-65536
+[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.094 s -- in com.thealgorithms.others.MandelbrotTest
+[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:  5.703 s
+[INFO] Finished at: 2026-11-11T17:41:01+05:30
+[INFO] ------------------------------------------------------------------------
diff --git a/work/R45-T016/result.txt b/work/R45-T016/result.txt
@@ -0,0 +1,3 @@
+command: mvn -B test -Dtest=MandelbrotTest -Dsurefire.failIfNoSpecifiedTests=false
+tests=3 failures/errors=0 skipped=0 records=13 mvn_exit=0
+status=PASS
diff --git a/work/R45-T016/tool_versions.txt b/work/R45-T016/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)]