6. Перевернуть связанный список [#161 #182935]

src/main/java/ru/j4j/collection/RevertLinked.java

@@ -0,0 +1,69 @@
+package ru.j4j.collection;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+public class RevertLinked<T> implements Iterable<T> {
+    private Node<T> head;
+
+    public void add(T value) {
+        Node<T> node = new Node<T>(value, null);
+        if (head == null) {
+            head = node;
+            return;
+        }
+        Node<T> tail = head;
+        while (tail.next != null) {
+            tail = tail.next;
+        }
+        tail.next = node;
+    }
+
+    public boolean revert() {
+        if (head == null || head.next == null) {
+            return false;
+        }
+        Node<T> current = head;
+        Node<T> prev = null;
+        while (current != null) {
+            head = current.next;
+            current.next = prev;
+            prev = current;
+            current = head;
+        }
+        head = prev;
+        return true;
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return new Iterator<T>() {
+            Node<T> node = head;
+
+            @Override
+            public boolean hasNext() {
+                return node != null;
+            }
+
+            @Override
+            public T next() {
+                if (!hasNext()) {
+                    throw new NoSuchElementException();
+                }
+                T value = node.value;
+                node = node.next;
+                return value;
+            }
+        };
+    }
+
+    private static class Node<T> {
+        T value;
+        Node<T> next;
+
+        public Node(T value, Node<T> next) {
+            this.value = value;
+            this.next = next;
+        }
+    }
+}

src/test/java/ru/j4j/collection/RevertLinkedTest.java

@@ -0,0 +1,37 @@
+package ru.j4j.collection;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RevertLinkedTest {
+    private RevertLinked<Integer> linked;
+
+    @BeforeEach
+    void init() {
+        linked = new RevertLinked<>();
+    }
+
+    @Test
+    void whenSize0ThenReturnFalse() {
+        assertThat(linked.revert()).isFalse();
+    }
+
+    @Test
+    void whenSize1ThenReturnFalse() {
+        linked.add(1);
+        assertThat(linked.revert()).isFalse();
+    }
+
+    @Test
+    void whenAddAndRevertTrue() {
+        linked.add(1);
+        linked.add(2);
+        linked.add(3);
+        linked.add(4);
+        assertThat(linked).containsSequence(1, 2, 3, 4);
+        assertThat(linked.revert()).isTrue();
+        assertThat(linked).containsSequence(4, 3, 2, 1);
+    }
+}