Merge branch 'master' into enhancement/#6336-comparision-sortUtils-logic

Author: dinishajais

DIRECTORY.md

@@ -304,6 +304,8 @@
           - 📄 [KadaneAlgorithm](src/main/java/com/thealgorithms/dynamicprogramming/KadaneAlgorithm.java)
           - 📄 [Knapsack](src/main/java/com/thealgorithms/dynamicprogramming/Knapsack.java)
           - 📄 [KnapsackMemoization](src/main/java/com/thealgorithms/dynamicprogramming/KnapsackMemoization.java)
+          - 📄 [KnapsackZeroOne](src/main/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOne.java)
+          - 📄 [KnapsackZeroOneTabulation](src/main/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOneTabulation.java)
           - 📄 [LevenshteinDistance](src/main/java/com/thealgorithms/dynamicprogramming/LevenshteinDistance.java)
           - 📄 [LongestAlternatingSubsequence](src/main/java/com/thealgorithms/dynamicprogramming/LongestAlternatingSubsequence.java)
           - 📄 [LongestArithmeticSubsequence](src/main/java/com/thealgorithms/dynamicprogramming/LongestArithmeticSubsequence.java)
@@ -1009,6 +1011,8 @@
           - 📄 [KadaneAlgorithmTest](src/test/java/com/thealgorithms/dynamicprogramming/KadaneAlgorithmTest.java)
           - 📄 [KnapsackMemoizationTest](src/test/java/com/thealgorithms/dynamicprogramming/KnapsackMemoizationTest.java)
           - 📄 [KnapsackTest](src/test/java/com/thealgorithms/dynamicprogramming/KnapsackTest.java)
+          - 📄 [KnapsackZeroOneTabulationTest](src/test/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOneTabulationTest.java)
+          - 📄 [KnapsackZeroOneTest](src/test/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOneTest.java)
           - 📄 [LevenshteinDistanceTests](src/test/java/com/thealgorithms/dynamicprogramming/LevenshteinDistanceTests.java)
           - 📄 [LongestAlternatingSubsequenceTest](src/test/java/com/thealgorithms/dynamicprogramming/LongestAlternatingSubsequenceTest.java)
           - 📄 [LongestArithmeticSubsequenceTest](src/test/java/com/thealgorithms/dynamicprogramming/LongestArithmeticSubsequenceTest.java)

src/main/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOne.java

@@ -0,0 +1,53 @@
+package com.thealgorithms.dynamicprogramming;
+
+/**
+ * The {@code KnapsackZeroOne} provides Recursive solution for the 0/1 Knapsack
+ * problem. Solves by exploring all combinations of items using recursion. No
+ * memoization or dynamic programming optimizations are applied.
+ *
+ * Time Complexity: O(2^n) — explores all subsets.
+ * Space Complexity: O(n) — due to recursive call stack.
+ *
+ * Problem Reference: https://en.wikipedia.org/wiki/Knapsack_problem
+ */
+public final class KnapsackZeroOne {
+
+    private KnapsackZeroOne() {
+        // Prevent instantiation
+    }
+
+    /**
+     * Solves the 0/1 Knapsack problem using recursion.
+     *
+     * @param values   the array containing values of the items
+     * @param weights  the array containing weights of the items
+     * @param capacity the total capacity of the knapsack
+     * @param n        the number of items
+     * @return the maximum total value achievable within the given weight limit
+     * @throws IllegalArgumentException if input arrays are null, empty, or
+     *     lengths mismatch
+     */
+    public static int compute(final int[] values, final int[] weights, final int capacity, final int n) {
+        if (values == null || weights == null) {
+            throw new IllegalArgumentException("Input arrays cannot be null.");
+        }
+        if (values.length != weights.length) {
+            throw new IllegalArgumentException("Value and weight arrays must be of the same length.");
+        }
+        if (capacity < 0 || n < 0) {
+            throw new IllegalArgumentException("Invalid input: arrays must be non-empty and capacity/n "
+                + "non-negative.");
+        }
+        if (n == 0 || capacity == 0 || values.length == 0) {
+            return 0;
+        }
+
+        if (weights[n - 1] <= capacity) {
+            final int include = values[n - 1] + compute(values, weights, capacity - weights[n - 1], n - 1);
+            final int exclude = compute(values, weights, capacity, n - 1);
+            return Math.max(include, exclude);
+        } else {
+            return compute(values, weights, capacity, n - 1);
+        }
+    }
+}

src/main/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOneTabulation.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.dynamicprogramming;
+
+/**
+ * Tabulation (Bottom-Up) Solution for 0-1 Knapsack Problem.
+ * This method uses dynamic programming to build up a solution iteratively,
+ * filling a 2-D array where each entry dp[i][w] represents the maximum value
+ * achievable with the first i items and a knapsack capacity of w.
+ *
+ * The tabulation approach is efficient because it avoids redundant calculations
+ * by solving all subproblems in advance and storing their results, ensuring
+ * each subproblem is solved only once. This is a key technique in dynamic programming,
+ * making it possible to solve problems that would otherwise be infeasible due to
+ * exponential time complexity in naive recursive solutions.
+ *
+ * Time Complexity: O(n * W), where n is the number of items and W is the knapsack capacity.
+ * Space Complexity: O(n * W) for the DP table.
+ *
+ * For more information, see:
+ * https://en.wikipedia.org/wiki/Knapsack_problem#Dynamic_programming
+ */
+public final class KnapsackZeroOneTabulation {
+
+    private KnapsackZeroOneTabulation() {
+        // Prevent instantiation
+    }
+
+    /**
+     * Solves the 0-1 Knapsack problem using the bottom-up tabulation technique.
+     * @param values the values of the items
+     * @param weights the weights of the items
+     * @param capacity the total capacity of the knapsack
+     * @param itemCount the number of items
+     * @return the maximum value that can be put in the knapsack
+     * @throws IllegalArgumentException if input arrays are null, of different lengths,or if capacity or itemCount is invalid
+     */
+    public static int compute(final int[] values, final int[] weights, final int capacity, final int itemCount) {
+        if (values == null || weights == null) {
+            throw new IllegalArgumentException("Values and weights arrays must not be null.");
+        }
+        if (values.length != weights.length) {
+            throw new IllegalArgumentException("Values and weights arrays must be non-null and of same length.");
+        }
+        if (capacity < 0) {
+            throw new IllegalArgumentException("Capacity must not be negative.");
+        }
+        if (itemCount < 0 || itemCount > values.length) {
+            throw new IllegalArgumentException("Item count must be between 0 and the length of the values array.");
+        }
+
+        final int[][] dp = new int[itemCount + 1][capacity + 1];
+
+        for (int i = 1; i <= itemCount; i++) {
+            final int currentValue = values[i - 1];
+            final int currentWeight = weights[i - 1];
+
+            for (int w = 1; w <= capacity; w++) {
+                if (currentWeight <= w) {
+                    final int includeItem = currentValue + dp[i - 1][w - currentWeight];
+                    final int excludeItem = dp[i - 1][w];
+                    dp[i][w] = Math.max(includeItem, excludeItem);
+                } else {
+                    dp[i][w] = dp[i - 1][w];
+                }
+            }
+        }
+
+        return dp[itemCount][capacity];
+    }
+}

src/test/java/com/thealgorithms/datastructures/lists/CountSinglyLinkedListRecursionTest.java

@@ -1,8 +1,10 @@
 package com.thealgorithms.datastructures.lists;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 public class CountSinglyLinkedListRecursionTest {
@@ -15,70 +17,112 @@ public void setUp() {
     }
 
     @Test
+    @DisplayName("Count of an empty list should be 0")
     public void testCountEmptyList() {
-        // An empty list should have a count of 0
-        assertEquals(0, list.count(), "Count of an empty list should be 0.");
+        assertEquals(0, list.count());
     }
 
     @Test
+    @DisplayName("Count after inserting a single element should be 1")
     public void testCountSingleElementList() {
-        // Insert a single element and check the count
         list.insert(1);
-        assertEquals(1, list.count(), "Count of a single-element list should be 1.");
+        assertEquals(1, list.count());
     }
 
     @Test
+    @DisplayName("Count after inserting multiple distinct elements")
     public void testCountMultipleElements() {
-        // Insert multiple elements and check the count
         for (int i = 1; i <= 5; i++) {
             list.insert(i);
         }
-        assertEquals(5, list.count(), "Count of a list with 5 elements should be 5.");
+        assertEquals(5, list.count());
     }
 
     @Test
+    @DisplayName("Count should reflect total number of nodes with duplicate values")
     public void testCountWithDuplicateElements() {
-        // Insert duplicate elements and verify the count is correct
-        list.insert(1);
         list.insert(2);
         list.insert(2);
         list.insert(3);
         list.insert(3);
-        assertEquals(5, list.count(), "Count of a list with duplicate elements should match total node count.");
+        list.insert(1);
+        assertEquals(5, list.count());
     }
 
     @Test
+    @DisplayName("Count should return 0 after clearing the list")
     public void testCountAfterClearingList() {
         for (int i = 1; i <= 4; i++) {
             list.insert(i);
         }
-        list.clear(); // assuming you have a clear method; if not, skip this
-        assertEquals(0, list.count(), "Count after clearing the list should be 0.");
+        list.clear(); // assumed to exist
+        assertEquals(0, list.count());
     }
 
     @Test
+    @DisplayName("Count on a very large list should be accurate")
     public void testCountOnVeryLargeList() {
         int n = 1000;
         for (int i = 0; i < n; i++) {
             list.insert(i);
         }
-        assertEquals(n, list.count(), "Count should correctly return for large list sizes.");
+        assertEquals(n, list.count());
     }
 
     @Test
+    @DisplayName("Count should work correctly with negative values")
     public void testCountOnListWithNegativeNumbers() {
         list.insert(-1);
-        list.insert(-5);
-        list.insert(-10);
-        assertEquals(3, list.count(), "Count should correctly handle negative values.");
+        list.insert(-2);
+        list.insert(-3);
+        assertEquals(3, list.count());
     }
 
     @Test
+    @DisplayName("Calling count multiple times should return the same value if list is unchanged")
     public void testCountIsConsistentWithoutModification() {
         list.insert(1);
         list.insert(2);
-        int firstCount = list.count();
-        int secondCount = list.count();
-        assertEquals(firstCount, secondCount, "Repeated count calls should return consistent values.");
+        int count1 = list.count();
+        int count2 = list.count();
+        assertEquals(count1, count2);
+    }
+
+    @Test
+    @DisplayName("Count should reflect total even if all values are the same")
+    public void testCountAllSameValues() {
+        for (int i = 0; i < 5; i++) {
+            list.insert(42);
+        }
+        assertEquals(5, list.count());
+    }
+
+    @Test
+    @DisplayName("Count should remain correct after multiple interleaved insert and count operations")
+    public void testCountAfterEachInsert() {
+        assertEquals(0, list.count());
+        list.insert(1);
+        assertEquals(1, list.count());
+        list.insert(2);
+        assertEquals(2, list.count());
+        list.insert(3);
+        assertEquals(3, list.count());
+    }
+
+    @Test
+    @DisplayName("List should not throw on edge count (0 nodes)")
+    public void testEdgeCaseNoElements() {
+        assertDoesNotThrow(() -> list.count());
+    }
+
+    @Test
+    @DisplayName("Should count accurately after inserting then removing all elements")
+    public void testCountAfterInsertAndClear() {
+        for (int i = 0; i < 10; i++) {
+            list.insert(i);
+        }
+        assertEquals(10, list.count());
+        list.clear();
+        assertEquals(0, list.count());
     }
 }

src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java

@@ -33,19 +33,19 @@ public void testDequeue() {
         queue.put(10);
         queue.put(20);
         queue.put(30);
-        assertEquals(10, queue.get()); // First item out
-        assertEquals(20, queue.get()); // Second item out
-        assertEquals(30, queue.get()); // Third item out
+        assertEquals(10, queue.get());
+        assertEquals(20, queue.get());
+        assertEquals(30, queue.get());
     }
 
     @Test
     public void testInterleavedOperations() {
         queue.put(10);
         queue.put(20);
-        assertEquals(10, queue.get()); // Dequeue first item
+        assertEquals(10, queue.get());
         queue.put(30);
-        assertEquals(20, queue.get()); // Dequeue second item
-        assertEquals(30, queue.get()); // Dequeue third item
+        assertEquals(20, queue.get());
+        assertEquals(30, queue.get());
     }
 
     @Test
@@ -62,8 +62,76 @@ public void testQueueSize() {
 
     @Test
     public void testEmptyQueueException() {
-        assertThrows(NoSuchElementException.class, () -> {
-            queue.get(); // Attempting to dequeue from empty queue
-        });
+        assertThrows(NoSuchElementException.class, () -> queue.get());
+    }
+
+    @Test
+    public void testDequeueAllElements() {
+        for (int i = 1; i <= 5; i++) {
+            queue.put(i);
+        }
+        for (int i = 1; i <= 5; i++) {
+            assertEquals(i, queue.get());
+        }
+        assertEquals(0, queue.size());
+    }
+
+    @Test
+    public void testLargeNumberOfOperations() {
+        int n = 1000;
+        for (int i = 0; i < n; i++) {
+            queue.put(i);
+        }
+        for (int i = 0; i < n; i++) {
+            assertEquals(i, queue.get());
+        }
+        assertEquals(0, queue.size());
+    }
+
+    @Test
+    public void testRefillDuringDequeue() {
+        queue.put(1);
+        queue.put(2);
+        assertEquals(1, queue.get());
+        queue.put(3);
+        queue.put(4);
+        assertEquals(2, queue.get());
+        assertEquals(3, queue.get());
+        assertEquals(4, queue.get());
+    }
+
+    @Test
+    public void testAlternatingPutAndGet() {
+        queue.put(1);
+        assertEquals(1, queue.get());
+        queue.put(2);
+        queue.put(3);
+        assertEquals(2, queue.get());
+        queue.put(4);
+        assertEquals(3, queue.get());
+        assertEquals(4, queue.get());
+    }
+
+    @Test
+    public void testSizeStability() {
+        queue.put(100);
+        int size1 = queue.size();
+        int size2 = queue.size();
+        assertEquals(size1, size2);
+    }
+
+    @Test
+    public void testMultipleEmptyDequeues() {
+        assertThrows(NoSuchElementException.class, () -> queue.get());
+        assertThrows(NoSuchElementException.class, () -> queue.get());
+    }
+
+    @Test
+    public void testQueueWithStrings() {
+        QueueByTwoStacks<String> stringQueue = new QueueByTwoStacks<>();
+        stringQueue.put("a");
+        stringQueue.put("b");
+        assertEquals("a", stringQueue.get());
+        assertEquals("b", stringQueue.get());
     }
 }