Merge branch 'master' into master

2020-10-16 18:50:44 +03:00
parent 0a9ccbfedd 969ae2bd2e
commit 0e5ddf4e4d
362 changed files with 5424 additions and 1074 deletions
@@ -9,4 +9,5 @@
 - [The Caesar Cipher in Java](https://www.baeldung.com/java-caesar-cipher)
 - [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
 - [Finding Top K Elements in an Array](https://www.baeldung.com/java-array-top-elements)
+- [Reversing a Linked List in Java](https://www.baeldung.com/java-reverse-linked-list)
 - More articles: [[<-- prev]](/algorithms-miscellaneous-5)
@@ -0,0 +1,30 @@
+package com.baeldung.algorithms.linkedlist;
+
+public class LinkedListReversal {
+
+    ListNode reverseList(ListNode head) {
+        ListNode previous = null;
+        ListNode current = head;
+        while (current != null) {
+            ListNode nextElement = current.getNext();
+            current.setNext(previous);
+            previous = current;
+            current = nextElement;
+        }
+        return previous;
+    }
+
+    ListNode reverseListRecursive(ListNode head) {
+        if (head == null) {
+            return null;
+        }
+        if (head.getNext() == null) {
+            return head;
+        }
+        ListNode node = reverseListRecursive(head.getNext());
+        head.getNext().setNext(head);
+        head.setNext(null);
+        return node;
+    }
+
+}
@@ -0,0 +1,28 @@
+package com.baeldung.algorithms.linkedlist;
+
+public class ListNode {
+
+    private int data;
+    private ListNode next;
+
+    ListNode(int data) {
+        this.data = data;
+        this.next = null;
+    }
+
+    public int getData() {
+        return data;
+    }
+
+    public ListNode getNext() {
+        return next;
+    }
+
+    public void setData(int data) {
+        this.data = data;
+    }
+
+    public void setNext(ListNode next) {
+        this.next = next;
+    }
+}
@@ -0,0 +1,59 @@
+package com.baeldung.algorithms.linkedlist;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+public class LinkedListReversalUnitTest {
+    @Test
+    public void givenLinkedList_whenIterativeReverse_thenOutputCorrectResult() {
+        ListNode head = constructLinkedList();
+        ListNode node = head;
+        for (int i = 1; i <= 5; i++) {
+            assertNotNull(node);
+            assertEquals(i, node.getData());
+            node = node.getNext();
+        }
+        LinkedListReversal reversal = new LinkedListReversal();
+        node = reversal.reverseList(head);
+        for (int i = 5; i >= 1; i--) {
+            assertNotNull(node);
+            assertEquals(i, node.getData());
+            node = node.getNext();
+        }
+    }
+
+    @Test
+    public void givenLinkedList_whenRecursiveReverse_thenOutputCorrectResult() {
+        ListNode head = constructLinkedList();
+        ListNode node = head;
+        for (int i = 1; i <= 5; i++) {
+            assertNotNull(node);
+            assertEquals(i, node.getData());
+            node = node.getNext();
+        }
+        LinkedListReversal reversal = new LinkedListReversal();
+        node = reversal.reverseListRecursive(head);
+        for (int i = 5; i >= 1; i--) {
+            assertNotNull(node);
+            assertEquals(i, node.getData());
+            node = node.getNext();
+        }
+    }
+
+    private ListNode constructLinkedList() {
+        ListNode head = null;
+        ListNode tail = null;
+        for (int i = 1; i <= 5; i++) {
+            ListNode node = new ListNode(i);
+            if (head == null) {
+                head = node;
+            } else {
+                tail.setNext(node);
+            }
+            tail = node;
+        }
+        return head;
+    }
+}