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https://github.com/TheAlgorithms/Java.git
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Enhance docs, remove main, add tests in ReverseStack
(#6018)
This commit is contained in:
@ -871,6 +871,7 @@
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* [TokenBucketTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/TokenBucketTest.java)
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* [TokenBucketTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/queues/TokenBucketTest.java)
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* stacks
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* stacks
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* [NodeStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java)
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* [NodeStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java)
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* [ReverseStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/ReverseStackTest.java)
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* [StackArrayListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayListTest.java)
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* [StackArrayListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayListTest.java)
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* [StackArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java)
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* [StackArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java)
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* [StackOfLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackOfLinkedListTest.java)
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* [StackOfLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/stacks/StackOfLinkedListTest.java)
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@ -1,10 +1,25 @@
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package com.thealgorithms.datastructures.stacks;
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package com.thealgorithms.datastructures.stacks;
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import java.util.Scanner;
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import java.util.Stack;
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import java.util.Stack;
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/**
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/**
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* Reversal of a stack using recursion.
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* Provides methods to reverse a stack using recursion.
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*
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* <p>This class includes methods to reverse the order of elements in a stack
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* without using additional data structures. Elements are inserted at the bottom
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* of the stack to achieve the reverse order.
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*
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* <p>Example usage:
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* <pre>
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* Stack<Integer> stack = new Stack<>();
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* stack.push(1);
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* stack.push(2);
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* stack.push(3);
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* ReverseStack.reverseStack(stack);
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* </pre>
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* After calling {@code reverseStack(stack)}, the stack's order is reversed.
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*
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* <p>This class is final and has a private constructor to prevent instantiation.
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*
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*
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* @author Ishika Agarwal, 2021
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* @author Ishika Agarwal, 2021
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*/
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*/
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@ -12,56 +27,48 @@ public final class ReverseStack {
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private ReverseStack() {
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private ReverseStack() {
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}
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}
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public static void main(String[] args) {
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/**
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try (Scanner sc = new Scanner(System.in)) {
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* Reverses the order of elements in the given stack using recursion.
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System.out.println("Enter the number of elements you wish to insert in the stack");
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* Steps:
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int n = sc.nextInt();
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* 1. Check if the stack is empty. If so, return.
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int i;
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* 2. Pop the top element from the stack.
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Stack<Integer> stack = new Stack<Integer>();
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* 3. Recursively reverse the remaining stack.
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System.out.println("Enter the stack elements");
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* 4. Insert the originally popped element at the bottom of the reversed stack.
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for (i = 0; i < n; i++) {
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*
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stack.push(sc.nextInt());
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* @param stack the stack to reverse; should not be null
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}
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*/
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reverseStack(stack);
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public static void reverseStack(Stack<Integer> stack) {
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System.out.println("The reversed stack is:");
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while (!stack.isEmpty()) {
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System.out.print(stack.peek() + ",");
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stack.pop();
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}
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}
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}
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private static void reverseStack(Stack<Integer> stack) {
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if (stack.isEmpty()) {
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if (stack.isEmpty()) {
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return;
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return;
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}
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}
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// Store the topmost element
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int element = stack.pop();
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int element = stack.peek();
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// Remove the topmost element
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stack.pop();
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// Reverse the stack for the leftover elements
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reverseStack(stack);
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reverseStack(stack);
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// Insert the topmost element to the bottom of the stack
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insertAtBottom(stack, element);
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insertAtBottom(stack, element);
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}
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}
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/**
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* Inserts the specified element at the bottom of the stack.
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*
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* <p>This method is a helper for {@link #reverseStack(Stack)}.
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*
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* Steps:
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* 1. If the stack is empty, push the element and return.
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* 2. Remove the top element from the stack.
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* 3. Recursively insert the new element at the bottom of the stack.
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* 4. Push the removed element back onto the stack.
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*
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* @param stack the stack in which to insert the element; should not be null
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* @param element the element to insert at the bottom of the stack
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*/
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private static void insertAtBottom(Stack<Integer> stack, int element) {
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private static void insertAtBottom(Stack<Integer> stack, int element) {
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if (stack.isEmpty()) {
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if (stack.isEmpty()) {
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// When stack is empty, insert the element so it will be present at
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// the bottom of the stack
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stack.push(element);
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stack.push(element);
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return;
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return;
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}
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}
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int ele = stack.peek();
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int topElement = stack.pop();
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// Keep popping elements till stack becomes empty. Push the elements
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// once the topmost element has moved to the bottom of the stack.
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stack.pop();
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insertAtBottom(stack, element);
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insertAtBottom(stack, element);
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stack.push(topElement);
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stack.push(ele);
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}
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}
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}
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}
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@ -0,0 +1,70 @@
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package com.thealgorithms.datastructures.stacks;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import java.util.Stack;
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import org.junit.jupiter.api.Test;
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class ReverseStackTest {
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@Test
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void testReverseEmptyStack() {
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Stack<Integer> stack = new Stack<>();
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ReverseStack.reverseStack(stack);
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assertTrue(stack.isEmpty(), "Reversing an empty stack should result in an empty stack.");
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}
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@Test
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void testReverseSingleElementStack() {
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Stack<Integer> stack = new Stack<>();
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stack.push(1);
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ReverseStack.reverseStack(stack);
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assertEquals(1, stack.peek(), "Reversing a single-element stack should have the same element on top.");
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}
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@Test
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void testReverseTwoElementStack() {
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Stack<Integer> stack = new Stack<>();
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stack.push(1);
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stack.push(2);
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ReverseStack.reverseStack(stack);
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assertEquals(1, stack.pop(), "After reversal, the stack's top element should be the first inserted element.");
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assertEquals(2, stack.pop(), "After reversal, the stack's next element should be the second inserted element.");
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}
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@Test
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void testReverseMultipleElementsStack() {
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Stack<Integer> stack = new Stack<>();
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stack.push(1);
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stack.push(2);
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stack.push(3);
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stack.push(4);
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ReverseStack.reverseStack(stack);
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assertEquals(1, stack.pop(), "Stack order after reversal should match the initial push order.");
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assertEquals(2, stack.pop());
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assertEquals(3, stack.pop());
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assertEquals(4, stack.pop());
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}
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@Test
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void testReverseStackAndVerifySize() {
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Stack<Integer> stack = new Stack<>();
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stack.push(10);
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stack.push(20);
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stack.push(30);
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stack.push(40);
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int originalSize = stack.size();
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ReverseStack.reverseStack(stack);
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assertEquals(originalSize, stack.size(), "Stack size should remain unchanged after reversal.");
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assertEquals(10, stack.pop(), "Reversal should place the first inserted element on top.");
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assertEquals(20, stack.pop());
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assertEquals(30, stack.pop());
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assertEquals(40, stack.pop());
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}
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}
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