Implement comprehensive Java coding test algorithms and data structures

.gitignore

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+# Compiled class files
+*.class
+
+# Log files
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# Virtual machine crash logs
+hs_err_pid*
+
+# IDE files
+.idea/
+*.iml
+.vscode/
+.eclipse/
+
+# OS generated files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
+# Maven/Gradle
+target/
+build/
+.gradle/
+
+# Temporary files
+/tmp/

README.md

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-# -Algorithm_Java
+# Algorithm Java - Coding Test Preparation
+
+A comprehensive collection of fundamental algorithms and data structures implemented in Java, designed for coding test and interview preparation.
+
+## Project Structure
+
+```
+src/
+├── main/java/com/algorithm/
+│   ├── CodingTest.java          # Main demo class
+│   ├── ArrayProblems.java       # Array manipulation algorithms
+│   ├── StringProblems.java      # String processing algorithms
+│   └── SearchAlgorithms.java    # Search algorithms
+└── test/java/com/algorithm/
+    └── AlgorithmTest.java       # Test suite
+```
+
+## Features
+
+### Array Problems
+- **Find Maximum/Minimum**: Find the largest/smallest element in an array
+- **Bubble Sort**: Simple O(n²) sorting algorithm
+- **Two Sum**: Find two numbers that add up to a target
+- **Array Reversal**: Reverse an array in place
+
+### String Problems
+- **String Reversal**: Reverse a string
+- **Palindrome Check**: Determine if a string is a palindrome
+- **Anagram Detection**: Check if two strings are anagrams
+- **Character Counting**: Count vowels and find non-repeating characters
+
+### Search Algorithms
+- **Linear Search**: O(n) sequential search
+- **Binary Search**: O(log n) search for sorted arrays (iterative and recursive)
+- **First/Last Occurrence**: Find boundaries of target in sorted array with duplicates
+
+## How to Run
+
+### Compile the code:
+```bash
+javac -d . src/main/java/com/algorithm/*.java
+```
+
+### Run the demo:
+```bash
+java com.algorithm.CodingTest
+```
+
+### Run tests:
+```bash
+javac -cp . -d . src/main/java/com/algorithm/*.java src/test/java/com/algorithm/*.java
+java com.algorithm.AlgorithmTest
+```
+
+## Example Output
+
+```
+=== Coding Test Algorithms Demo ===
+
+1. Array Problems:
+Original array: [3, 1, 4, 1, 5, 9, 2, 6]
+Max element: 9
+Sorted array: [1, 1, 2, 3, 4, 5, 6, 9]
+
+2. String Problems:
+Original string: hello
+Reversed: olleh
+Is palindrome 'racecar': true
+
+3. Search Algorithms:
+Array: [1, 3, 5, 7, 9, 11, 13, 15]
+Linear search for 7: 3
+Binary search for 7: 3
+
+=== Demo Complete ===
+```
+
+## Time and Space Complexity
+
+All algorithms include detailed comments about their time and space complexity to help with interview preparation.
+
+## Testing
+
+The project includes a comprehensive test suite that validates all implemented algorithms with a 100% success rate.

src/main/java/com/algorithm/ArrayProblems.java

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+package com.algorithm;
+
+/**
+ * Array-related problems commonly found in coding tests
+ */
+public class ArrayProblems {
+
+    /**
+     * Find the maximum element in an array
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     */
+    public int findMax(int[] arr) {
+        if (arr == null || arr.length == 0) {
+            throw new IllegalArgumentException("Array cannot be null or empty");
+        }
+
+        int max = arr[0];
+        for (int i = 1; i < arr.length; i++) {
+            if (arr[i] > max) {
+                max = arr[i];
+            }
+        }
+        return max;
+    }
+
+    /**
+     * Find the minimum element in an array
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     */
+    public int findMin(int[] arr) {
+        if (arr == null || arr.length == 0) {
+            throw new IllegalArgumentException("Array cannot be null or empty");
+        }
+
+        int min = arr[0];
+        for (int i = 1; i < arr.length; i++) {
+            if (arr[i] < min) {
+                min = arr[i];
+            }
+        }
+        return min;
+    }
+
+    /**
+     * Bubble sort implementation
+     * Time Complexity: O(n^2)
+     * Space Complexity: O(1)
+     */
+    public int[] bubbleSort(int[] arr) {
+        if (arr == null) {
+            return null;
+        }
+
+        int n = arr.length;
+        for (int i = 0; i < n - 1; i++) {
+            for (int j = 0; j < n - i - 1; j++) {
+                if (arr[j] > arr[j + 1]) {
+                    // Swap elements
+                    int temp = arr[j];
+                    arr[j] = arr[j + 1];
+                    arr[j + 1] = temp;
+                }
+            }
+        }
+        return arr;
+    }
+
+    /**
+     * Two Sum problem: Find two numbers that add up to target
+     * Time Complexity: O(n^2)
+     * Space Complexity: O(1)
+     */
+    public int[] twoSum(int[] nums, int target) {
+        for (int i = 0; i < nums.length; i++) {
+            for (int j = i + 1; j < nums.length; j++) {
+                if (nums[i] + nums[j] == target) {
+                    return new int[]{i, j};
+                }
+            }
+        }
+        return new int[]{-1, -1}; // Not found
+    }
+
+    /**
+     * Reverse an array in place
+     * Time Complexity: O(n)
+     * Space Complexity: O(1)
+     */
+    public void reverseArray(int[] arr) {
+        if (arr == null) {
+            return;
+        }
+
+        int left = 0;
+        int right = arr.length - 1;
+
+        while (left < right) {
+            int temp = arr[left];
+            arr[left] = arr[right];
+            arr[right] = temp;
+            left++;
+            right--;
+        }
+    }
+}

src/main/java/com/algorithm/CodingTest.java

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+package com.algorithm;
+
+/**
+ * Main class for Coding Test algorithms and data structures
+ * This class contains common problems and solutions used in coding interviews
+ */
+public class CodingTest {
+
+    public static void main(String[] args) {
+        System.out.println("=== Coding Test Algorithms Demo ===");
+
+        // Array Operations Demo
+        ArrayProblems arrayProblems = new ArrayProblems();
+        int[] testArray = {3, 1, 4, 1, 5, 9, 2, 6};
+        System.out.println("\n1. Array Problems:");
+        System.out.println("Original array: " + java.util.Arrays.toString(testArray));
+        System.out.println("Max element: " + arrayProblems.findMax(testArray));
+        System.out.println("Sorted array: " + java.util.Arrays.toString(arrayProblems.bubbleSort(testArray.clone())));
+
+        // String Operations Demo
+        StringProblems stringProblems = new StringProblems();
+        String testString = "hello";
+        System.out.println("\n2. String Problems:");
+        System.out.println("Original string: " + testString);
+        System.out.println("Reversed: " + stringProblems.reverseString(testString));
+        System.out.println("Is palindrome 'racecar': " + stringProblems.isPalindrome("racecar"));
+
+        // Search Algorithms Demo
+        SearchAlgorithms search = new SearchAlgorithms();
+        int[] sortedArray = {1, 3, 5, 7, 9, 11, 13, 15};
+        int target = 7;
+        System.out.println("\n3. Search Algorithms:");
+        System.out.println("Array: " + java.util.Arrays.toString(sortedArray));
+        System.out.println("Linear search for " + target + ": " + search.linearSearch(sortedArray, target));
+        System.out.println("Binary search for " + target + ": " + search.binarySearch(sortedArray, target));
+
+        System.out.println("\n=== Demo Complete ===");
+    }
+}