diff --git a/DIRECTORY.md b/DIRECTORY.md index 1cd30a336f24..228735aa8ea9 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -170,6 +170,7 @@ * [LinkedQueue](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/LinkedQueue.java) * [PriorityQueues](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/PriorityQueues.java) * [Queue](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/Queue.java) + * [QueueByTwoStacks](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/queues/QueueByTwoStacks.java) * stacks * [NodeStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/NodeStack.java) * [ReverseStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/stacks/ReverseStack.java) @@ -477,6 +478,7 @@ * searches * [BinarySearch](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/BinarySearch.java) * [BinarySearch2dArray](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/BinarySearch2dArray.java) + * [BM25InvertedIndex](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/BM25InvertedIndex.java) * [BreadthFirstSearch](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/BreadthFirstSearch.java) * [DepthFirstSearch](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/DepthFirstSearch.java) * [ExponentalSearch](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/ExponentalSearch.java) @@ -731,6 +733,7 @@ * [GenericArrayListQueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/GenericArrayListQueueTest.java) * [LinkedQueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/LinkedQueueTest.java) * [PriorityQueuesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/PriorityQueuesTest.java) + * [QueueByTwoStacksTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java) * [QueueTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/QueueTest.java) * stacks * [LinkedListStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/LinkedListStackTest.java) @@ -756,7 +759,7 @@ * [SplayTreeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/SplayTreeTest.java) * [TreapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreapTest.java) * [TreeTestUtils](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreeTestUtils.java) - * [TrieImpTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TrieImpTest.java) + * [TrieTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TrieTest.java) * [VerticalOrderTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/VerticalOrderTraversalTest.java) * [ZigzagTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/ZigzagTraversalTest.java) * divideandconquer @@ -887,6 +890,7 @@ * [PrimeFactorizationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PrimeFactorizationTest.java) * [PronicNumberTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PronicNumberTest.java) * [PythagoreanTripleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/PythagoreanTripleTest.java) + * [QuadraticEquationSolverTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/QuadraticEquationSolverTest.java) * [ReverseNumberTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/ReverseNumberTest.java) * [SecondMinMaxTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/SecondMinMaxTest.java) * [SieveOfEratosthenesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/SieveOfEratosthenesTest.java) @@ -952,6 +956,7 @@ * [SRTFSchedulingTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/scheduling/SRTFSchedulingTest.java) * searches * [BinarySearch2dArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/BinarySearch2dArrayTest.java) + * [BM25InvertedIndexTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/BM25InvertedIndexTest.java) * [BreadthFirstSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/BreadthFirstSearchTest.java) * [DepthFirstSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/DepthFirstSearchTest.java) * [HowManyTimesRotatedTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/HowManyTimesRotatedTest.java) diff --git a/src/main/java/com/thealgorithms/datastructures/queues/QueueByTwoStacks.java b/src/main/java/com/thealgorithms/datastructures/queues/QueueByTwoStacks.java new file mode 100644 index 000000000000..11e5e9b83892 --- /dev/null +++ b/src/main/java/com/thealgorithms/datastructures/queues/QueueByTwoStacks.java @@ -0,0 +1,87 @@ +package com.thealgorithms.datastructures.queues; + +import java.util.NoSuchElementException; +import java.util.Stack; + +/** + * A queue implementation using two stacks. This class provides methods to + * enqueue (add) elements to the end of the queue and dequeue (remove) + * elements from the front, while utilizing two internal stacks to manage + * the order of elements. + * + * @param The type of elements held in this queue. + */ +public class QueueByTwoStacks { + + private final Stack enqueueStk; + private final Stack dequeueStk; + + /** + * Constructor that initializes two empty stacks for the queue. + * The `enqueueStk` is used to push elements when enqueuing, and + * the `dequeueStk` is used to pop elements when dequeuing. + */ + public QueueByTwoStacks() { + enqueueStk = new Stack<>(); + dequeueStk = new Stack<>(); + } + + /** + * Adds an element to the end of the queue. This method pushes the element + * onto the `enqueueStk`. + * + * @param item The element to be added to the queue. + */ + public void put(T item) { + enqueueStk.push(item); + } + + /** + * Removes and returns the element at the front of the queue. + * If `dequeueStk` is empty, it transfers all elements from + * `enqueueStk` to `dequeueStk` to maintain the correct FIFO + * (First-In-First-Out) order before popping. + * + * @return The element at the front of the queue. + * @throws NoSuchElementException If the queue is empty. + */ + public T get() { + if (dequeueStk.isEmpty()) { + while (!enqueueStk.isEmpty()) { + dequeueStk.push(enqueueStk.pop()); + } + } + if (dequeueStk.isEmpty()) { + throw new NoSuchElementException("Queue is empty"); + } + return dequeueStk.pop(); + } + + /** + * Returns the total number of elements currently in the queue. + * This is the sum of the sizes of both stacks. + * + * @return The number of elements in the queue. + */ + public int size() { + return enqueueStk.size() + dequeueStk.size(); + } + + /** + * Returns a string representation of the queue, showing the elements + * in the correct order (from front to back). + * The `dequeueStk` is first cloned, and then all elements from the + * `enqueueStk` are added to the cloned stack in reverse order to + * represent the queue accurately. + * + * @return A string representation of the queue. + */ + @Override + public String toString() { + Stack tempStack = (Stack) dequeueStk.clone(); + while (!enqueueStk.isEmpty()) { + tempStack.push(enqueueStk.pop()); + } + return "Queue(" + tempStack + ")"; + } +} diff --git a/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java b/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java new file mode 100644 index 000000000000..87f136a84631 --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/queues/QueueByTwoStacksTest.java @@ -0,0 +1,69 @@ +package com.thealgorithms.datastructures.queues; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import java.util.NoSuchElementException; +import org.junit.jupiter.api.BeforeEach; +import org.junit.jupiter.api.Test; + +public class QueueByTwoStacksTest { + + private QueueByTwoStacks queue; + + @BeforeEach + public void setUp() { + queue = new QueueByTwoStacks<>(); + } + + @Test + public void testEmptyQueue() { + assertEquals(0, queue.size()); + } + + @Test + public void testEnqueue() { + queue.put(10); + queue.put(20); + assertEquals(2, queue.size()); + } + + @Test + 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 + } + + @Test + public void testInterleavedOperations() { + queue.put(10); + queue.put(20); + assertEquals(10, queue.get()); // Dequeue first item + queue.put(30); + assertEquals(20, queue.get()); // Dequeue second item + assertEquals(30, queue.get()); // Dequeue third item + } + + @Test + public void testQueueSize() { + assertEquals(0, queue.size()); + queue.put(1); + assertEquals(1, queue.size()); + queue.put(2); + queue.put(3); + assertEquals(3, queue.size()); + queue.get(); + assertEquals(2, queue.size()); + } + + @Test + public void testEmptyQueueException() { + assertThrows(NoSuchElementException.class, () -> { + queue.get(); // Attempting to dequeue from empty queue + }); + } +}