Merge pull request #99 from exercism/new-exercise-simple-linked-list

Add new exercise simple linked list

.gitignore

@@ -9,3 +9,4 @@ build/
 bin/configlet
 bin/configlet.exe
 gradle/
+/exercises/.nb-gradle/

config.json

@@ -38,6 +38,7 @@
     "octal",
     "luhn",
     "pig-latin",
+    "simple-linked-list",
     "linked-list",
     "nth-prime",
     "pascals-triangle"

exercises/settings.gradle

@@ -30,6 +30,7 @@ include 'prime-factors'
 include 'scrabble-score'
 include 'sieve'
 include 'simple-cipher'
+include 'simple-linked-list'
 include 'space-age'
 include 'strain'
 include 'triangle'

exercises/simple-linked-list/build.gradle

@@ -0,0 +1,12 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.10"
+  testCompile "org.assertj:assertj-core:3.2.0"
+}

exercises/simple-linked-list/src/example/java/SimpleLinkedList.java

@@ -0,0 +1,85 @@
+
+import java.lang.reflect.Array;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+
+public class SimpleLinkedList<T> {
+
+    private static class Element<T> {
+
+        final T value;
+        Element next;
+
+        Element(T value) {
+            this.value = value;
+        }
+    }
+
+    private Element<T> head;
+    private int size;
+
+    public SimpleLinkedList() {
+    }
+
+    public SimpleLinkedList(T[] values) {
+        for (int ii = values.length - 1; ii >= 0; ii--) {
+            push(values[ii]);
+        }
+    }
+
+    public final void push(T value) {
+        Element<T> newElement = new Element<>(value);
+        this.size++;
+        if (Objects.isNull(head)) {
+            head = newElement;
+        } else {
+            newElement.next = head;
+            head = newElement;
+        }
+    }
+
+    public T pop() {
+        if (Objects.isNull(head)) {
+            throw new NoSuchElementException();
+        }
+        T value = head.value;
+        head = head.next;
+        this.size--;
+        return value;
+    }
+
+    public void reverse() {
+        Element<T> current = head;
+        Element<T> next;
+        Element<T> previous = null;
+        while (Objects.nonNull(current)) {
+            next = current.next;
+            current.next = previous;
+            previous = current;
+            current = next;
+        }
+        head = previous;
+    }
+
+    public T[] asArray(Class<T> clazz) {
+        T[] result = newArray(clazz, this.size);
+        int index = 0;
+        Element<T> current = head;
+        while (Objects.nonNull(current)) {
+            result[index++] = current.value;
+            current = current.next;
+        }
+        return result;
+    }
+
+    private <T> T[] newArray(Class<T> clazz, int size) {
+        @SuppressWarnings("unchecked")
+        T[] arr = (T[]) Array.newInstance(clazz, size);
+
+        return arr;
+    }
+
+    public int size() {
+        return this.size;
+    }
+}

exercises/simple-linked-list/src/test/java/SimpleLinkedListTest.java

@@ -0,0 +1,73 @@
+
+import java.util.NoSuchElementException;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class SimpleLinkedListTest {
+
+    @Test
+    public void aNewListIsEmpty() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        assertThat(list.size()).isEqualTo(0);
+    }
+
+    @Test
+    public void canCreateFromArray() {
+        Integer[] values = new Integer[]{1, 2, 3};
+        SimpleLinkedList list = new SimpleLinkedList(values);
+        assertThat(list.size()).isEqualTo(3);
+    }
+
+    @Test(expected = NoSuchElementException.class)
+    public void popOnEmptyListWillThrow() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        list.pop();
+    }
+
+    @Test
+    public void popReturnsLastAddedElement() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        list.push(9);
+        list.push(8);
+        assertThat(list.size()).isEqualTo(2);
+        assertThat(list.pop()).isEqualTo(8);
+        assertThat(list.pop()).isEqualTo(9);
+        assertThat(list.size()).isEqualTo(0);
+    }
+
+    @Test
+    public void reverseReversesList() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        list.push(9);
+        list.push(8);
+        list.push(7);
+        list.push(6);
+        list.push(5);
+        list.reverse();
+        assertThat(list.pop()).isEqualTo(9);
+        assertThat(list.pop()).isEqualTo(8);
+        assertThat(list.pop()).isEqualTo(7);
+        assertThat(list.pop()).isEqualTo(6);
+        assertThat(list.pop()).isEqualTo(5);
+    }
+
+    @Test
+    public void canReturnListAsArray() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        list.push(9);
+        list.push(8);
+        list.push(7);
+        list.push(6);
+        list.push(5);
+        Integer[] expected = {5, 6, 7, 8, 9};
+        assertThat(list.asArray(Integer.class)).containsExactly(expected);
+    }
+
+    @Test
+    public void canReturnEmptyListAsEmptyArray() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        Object[] expected = {};
+        assertThat(list.asArray(Object.class)).containsExactly(expected);
+    }
+
+}