Add new exercise simple-linked-list

Author: matthewmorgan

.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 +1,75 @@
+import java.util.NoSuchElementException;
+import java.util.Objects;
+
+public class SimpleLinkedList {
+
+    class Element {
+
+        int value;
+        Element next;
+
+        Element(int value) {
+            this.value = value;
+        }
+    }
+
+    private Element head;
+    private int size;
+
+    public SimpleLinkedList() {}
+
+    public SimpleLinkedList(int[] values) {
+        for (int ii = values.length - 1; ii >= 0; ii--) {
+            push(values[ii]);
+        }
+    }
+
+    public void push(int value) {
+        Element newElement = new Element(value);
+        this.size++;
+        if (Objects.isNull(head)) {
+            head = newElement;
+        } else {
+            newElement.next = head;
+            head = newElement;
+        }
+    }
+
+    public int pop() {
+        if (Objects.isNull(head)) {
+            throw new NoSuchElementException();
+        }
+        int value = head.value;
+        head = head.next;
+        this.size--;
+        return value;
+    }
+
+    public void reverse() {
+        Element current = head;
+        Element next;
+        Element previous = null;
+        while (Objects.nonNull(current)) {
+            next = current.next;
+            current.next = previous;
+            previous = current;
+            current = next;
+        }
+        head = previous;
+    }
+
+    public int[] asArray() {
+        int[] result = new int[size];
+        int index = 0;
+        Element current = head;
+        while (Objects.nonNull(current)) {
+            result[index++] = current.value;
+            current = current.next;
+        }
+        return result;
+    }
+
+    public int size() {
+        return this.size;
+    }
+}

exercises/simple-linked-list/src/main/java/.keep

@@ -0,0 +1,71 @@
+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() {
+        int[] values = new int[]{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);
+        int[] expected = {5, 6, 7, 8, 9};
+        assertThat(list.asArray()).containsExactly(expected);
+    }
+
+    @Test
+    public void canReturnEmptyListAsEmptyArray() {
+        SimpleLinkedList list = new SimpleLinkedList();
+        int[] expected = {};
+        assertThat(list.asArray()).containsExactly(expected);
+    }
+}