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docs: Expand FAANG-style interview Q&A with detailed answers and code for CountingError
WHAT the file contains: - An HTML document with **interview-style questions + detailed answers** about the `CountingError` code. - Covers multiple aspects: array traversal, string operations, robustness, optimization, behavior changes, design, and testing. - Includes inline **Java code snippets** demonstrating solutions and best practices. WHY this matters: - Transforms abstract questions into a full **study guide** with explanations and code. - Provides practical insights into error handling, optimization, and extensibility. - Serves as both an interview prep resource and a reference for improving Java code quality. HOW it is structured: 1. Sections are grouped by topic (Logic, Strings, Edge Cases, Optimization, Extensions, Design). 2. Each question is followed by an `<p class="answer">` explanation or `<pre class="code">` snippet. 3. HTML styling improves readability with Comic Sans for text and monospace for code. 4. Includes **unit tests** to demonstrate validation of the `count()` method. Tips & gotchas: - `Comic Sans MS` font may not be ideal for technical documents → consider monospace or standard sans-serif. - Uses HTML 4.01 strict DTD → modern HTML5 would provide better compatibility. - Answers assume Java knowledge (indexOf, startsWith, streams, null handling). - Some optimizations (parallel streams) trade readability for performance. Use-cases: - Interview preparation for FAANG-style coding and system design rounds. - Classroom material to teach **robust Java string/array handling**. - A reference document for writing safe, testable, and maintainable code. - Ready-made Q&A for mock interview practice. Short key: docs-counting error-interview-qa-expanded. Signed-off-by: https://github.com/Someshdiwan <[email protected]>
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‎Section8LoopAB/Loop 2.O/src/CountingErrorsANS.html‎

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta http-equiv="Content-Style-Type" content="text/css">
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<title>FAANG Interview Questions - CountingError Analysis</title>
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<meta name="Author" content="AI Assistant">
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<meta name="Generator" content="IntelliJ IDEA">
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<style type="text/css">
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p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 18.0px 'Comic Sans MS'; -webkit-text-stroke: #000000}
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p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 18.0px 'Comic Sans MS'; color: #6d6d6d; -webkit-text-stroke: #6d6d6d; min-height: 25.0px}
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p.answer {margin: 0.0px 0.0px 0.0px 20.0px; font: 16.0px 'Comic Sans MS'; color: #2c2c2c;}
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li.li1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 18.0px 'Comic Sans MS'; -webkit-text-stroke: #000000}
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span.s1 {font-kerning: none}
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ol.ol1 {list-style-type: decimal}
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pre.code {background-color: #f5f5f5; padding: 10px; border-radius: 5px; font: 14px Monaco, monospace;}
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</style>
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</head>
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<body>
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<p class="p1"><span class="s1"><b>🚀 FAANG-Style Interview Questions on the CountingError Code</b></span></p>
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<p class="p1"><span class="s1"><b>✅ Logic & Array Traversal</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>How does the count() method traverse the 2D array?</b></span></li>
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<p class="answer">The method uses nested loops for row-major traversal. The outer loop iterates through rows (0 to things.length-1), while the inner loop iterates through columns (0 to things[r].length-1). This creates a left-to-right, top-to-bottom traversal pattern.</p>
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<li class="li1"><span class="s1"><b>What about jagged arrays?</b></span></li>
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<p class="answer">The code handles jagged arrays correctly because it uses things[r].length for each row separately, adapting to different row lengths dynamically.</p>
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<li class="li1"><span class="s1"><b>Explain indexOf("a") >= 0</b></span></li>
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<p class="answer">indexOf() returns -1 if the character isn't found, and the actual index (0 or greater) if found. Using >= 0 checks for the presence of 'a' anywhere in the string, while == 0 would only match strings starting with 'a'.</p>
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</ol>
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<p class="p1"><span class="s1"><b>✅ String Operations</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>indexOf() Internal Performance</b></span></li>
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<p class="answer">indexOf() performs a linear search with O(n) time complexity, where n is the string length. It scans characters sequentially until finding a match or reaching the end.</p>
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<li class="li1"><span class="s1"><b>Multiple 'a' Characters</b></span></li>
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<p class="answer">To count strings with multiple 'a' characters:</p>
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<pre class="code">if (things[r][c].length() - things[r][c].replace("a", "").length() > 1)</pre>
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<li class="li1"><span class="s1"><b>Strings Starting with 'a'</b></span></li>
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<p class="answer">To check for strings starting with 'a':</p>
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<pre class="code">if (things[r][c].startsWith("a"))</pre>
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</ol>
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<!-- Continue with other sections similarly -->
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<p class="p1"><span class="s1"><b>✅ Robustness & Edge Cases</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>Null Values</b></span></li>
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<p class="answer">The current code will throw NullPointerException for null array input, null rows, or null string elements. This needs to be handled with proper null checks.</p>
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<li class="li1"><span class="s1"><b>Null-Safe Solution</b></span></li>
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<pre class="code">
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public static int count(String[][] things) {
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if (things == null) return 0;
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int count = 0;
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for (String[] row : things) {
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if (row != null) {
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for (String str : row) {
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if (str != null && str.indexOf("a") >= 0) {
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count++;
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}
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}
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}
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}
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return count;
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}</pre>
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<li class="li1"><span class="s1"><b>Empty Array</b></span></li>
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<p class="answer">For an empty array (new String[0][0]), the method correctly returns 0 as there are no strings to count.</p>
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</ol>
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<p class="p1"><span class="s1"><b>✅ Optimization</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>Performance Improvements</b></span></li>
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<p class="answer">For large datasets, we can improve efficiency by:</p>
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<ul class="answer">
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<li>Using enhanced for loops</li>
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<li>Implementing parallel processing</li>
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<li>Early termination when possible</li>
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<li>Avoiding unnecessary string operations</li>
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</ul>
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<li class="li1"><span class="s1"><b>Set&lt;Character&gt; Usage</b></span></li>
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<p class="answer">Using a Set&lt;Character&gt; would be unnecessary overhead for checking a single character 'a'. However, it would be beneficial when checking for multiple characters like vowels.</p>
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<li class="li1"><span class="s1"><b>Parallel Processing</b></span></li>
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<pre class="code">
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public static int countParallel(String[][] things) {
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if (things == null) return 0;
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return Arrays.stream(things)
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.parallel()
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.flatMap(Arrays::stream)
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.filter(s -> s != null && s.indexOf("a") >= 0)
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.mapToInt(s -> 1)
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.sum();
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}</pre>
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</ol>
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<p class="p1"><span class="s1"><b>✅ Code Extension / Behavior Change</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>Count Vowels</b></span></li>
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<pre class="code">
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public static int countVowels(String[][] things) {
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if (things == null) return 0;
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String vowels = "aeiou";
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int count = 0;
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for (String[] row : things) {
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if (row != null) {
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for (String str : row) {
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if (str != null &&
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vowels.chars().anyMatch(v -> str.indexOf(v) >= 0)) {
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count++;
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}
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}
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}
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}
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return count;
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}</pre>
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<li class="li1"><span class="s1"><b>Case-Insensitive Matching</b></span></li>
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<p class="answer">To make the method case-insensitive:</p>
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<pre class="code">if (str != null && str.toLowerCase().indexOf("a") >= 0)</pre>
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<li class="li1"><span class="s1"><b>Return List Instead of Count</b></span></li>
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<pre class="code">
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public static List&lt;String&gt; findStringsWithA(String[][] things) {
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List&lt;String&gt; result = new ArrayList&lt;&gt;();
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if (things == null) return result;
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for (String[] row : things) {
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if (row != null) {
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for (String str : row) {
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if (str != null && str.indexOf("a") >= 0) {
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result.add(str);
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}
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}
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}
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}
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return result;
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}</pre>
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</ol>
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<p class="p1"><span class="s1"><b>✅ Design & Readability</b></span></p>
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<ol class="ol1">
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<li class="li1"><span class="s1"><b>Code Refactoring</b></span></li>
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<p class="answer">Suggested improvements:</p>
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<ul class="answer">
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<li>Add comprehensive input validation</li>
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<li>Use meaningful variable names</li>
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<li>Extract character checking logic to separate method</li>
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<li>Add JavaDoc documentation</li>
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<li>Consider using modern Java features like streams</li>
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</ul>
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<li class="li1"><span class="s1"><b>Method Naming</b></span></li>
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<p class="answer">Better method names would be:</p>
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<ul class="answer">
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<li>countStringsContaining()</li>
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<li>countStringsWithCharacter()</li>
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<li>countMatchingStrings()</li>
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</ul>
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<li class="li1"><span class="s1"><b>Unit Testing</b></span></li>
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<pre class="code">
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@Test
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public void testCount() {
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// Test regular case
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String[][] normal = {{"apple", "banana"}, {"cat", "dog"}};
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assertEquals(2, CountingError.count(normal));
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// Test empty array
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String[][] empty = new String[0][0];
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assertEquals(0, CountingError.count(empty));
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// Test null array
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assertDoesNotThrow(() -> CountingError.count(null));
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// Test array with nulls
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String[][] withNulls = {null, {"apple", null}};
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assertDoesNotThrow(() -> CountingError.count(withNulls));
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// Test case sensitivity
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String[][] mixed = {{"Apple", "BANANA"}};
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assertEquals(1, CountingError.count(mixed));
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}</pre>
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</ol>
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<p class="p2"><span class="s1"></span><br></p>
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<p class="p1"><span class="s1"><b>📝 Additional Notes</b></span></p>
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<p class="answer">
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• All code examples include proper error handling<br>
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• Solutions focus on both functionality and maintainability<br>
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• Performance considerations are balanced with code readability<br>
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• Test cases cover edge cases and common scenarios<br>
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</p>
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</body>
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</html>

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