strain exercise

config.json

@@ -22,7 +22,8 @@
     "binary",
     "prime-factors",
     "raindrops",
-    "allergies"
+    "allergies",
+    "strain"
   ],
   "deprecated": [
   ],

strain/build.gradle

@@ -0,0 +1,11 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.10"
+}

strain/example.java

@@ -0,0 +1,16 @@
+import java.util.Collection;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class Strain {
+
+	public static <T> Collection<T> keep(Collection<T> coll, Predicate<T> func)
+	{
+		return coll.stream().filter(func).collect(Collectors.toList());
+	}
+	
+	public static <T> Collection<T> discard(Collection<T> coll, Predicate<T> func)
+	{
+		return coll.stream().filter(func.negate()).collect(Collectors.toList());
+	}
+}

strain/src/main/java/example.java

@@ -0,0 +1,2 @@
+public class Strain {
+}

strain/src/test/java/StrainTest.java

@@ -0,0 +1,123 @@
+package strain;
+
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.List;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class StrainTest {
+
+	@Test
+	public void emptyKeep() {
+		List<Integer> expected = new LinkedList<>();
+		List<Integer> test = new LinkedList<>();
+		Assert.assertEquals(expected, Strain.keep(test, x -> x < 10));
+	}
+
+	@Test
+	public void keepEverything() {
+		List<Integer> expected = Arrays.asList(1, 2, 3);
+		List<Integer> test = Arrays.asList(1, 2, 3);
+		Assert.assertEquals(expected, Strain.keep(test, x -> x < 10));
+	}
+
+	@Test
+	public void keepFirstAndLast() {
+		List<Integer> expected = Arrays.asList(1, 3);
+		List<Integer> test = Arrays.asList(1, 2, 3);
+		Assert.assertEquals(expected, Strain.keep(test, x -> x % 2 != 0));
+	}
+
+	@Test
+	public void keepNeitherFirstNorLast() {
+		List<Integer> expected = Arrays.asList(2, 4);
+		List<Integer> test = Arrays.asList(1, 2, 3, 4, 5);
+		Assert.assertEquals(expected, Strain.keep(test, x -> x % 2 == 0));
+	}
+
+	@Test
+	public void KeepStrings() {
+		List<String> words = Arrays
+				.asList("apple zebra banana zombies cherimoya zelot".split(" "));
+		List<String> expected = Arrays.asList("zebra", "zombies", "zelot");
+		Assert.assertEquals(expected,
+				Strain.keep(words, x -> x.startsWith("z")));
+	}
+
+	@Test
+	public void KeepArrays() {
+		List<List<Integer>> actual = Arrays.asList(
+				Arrays.asList(1, 2, 3),
+				Arrays.asList(5, 5, 5), 
+				Arrays.asList(5, 1, 2),
+				Arrays.asList(2, 1, 2), 
+				Arrays.asList(1, 5, 2),
+				Arrays.asList(2, 2, 1), 
+				Arrays.asList(1, 2, 5));
+		List<List<Integer>> expected = Arrays.asList(
+				Arrays.asList(5, 5, 5),
+				Arrays.asList(5, 1, 2), 
+				Arrays.asList(1, 5, 2),
+				Arrays.asList(1, 2, 5));
+		Assert.assertEquals(expected,
+				Strain.keep(actual, col -> col.contains(5)));
+	}
+
+	@Test
+	public void emptyDiscard() {
+		List<Integer> expected = new LinkedList<>();
+		List<Integer> test = new LinkedList<>();
+		Assert.assertEquals(expected, Strain.discard(test, x -> x < 10));
+	}
+
+	@Test
+	public void discardNothing() {
+		List<Integer> expected = Arrays.asList(1, 2, 3);
+		List<Integer> test = Arrays.asList(1, 2, 3);
+		Assert.assertEquals(expected, Strain.discard(test, x -> x > 10));
+	}
+
+	@Test
+	public void discardFirstAndLast() {
+		List<Integer> expected = Arrays.asList(2);
+		List<Integer> test = Arrays.asList(1, 2, 3);
+		Assert.assertEquals(expected, Strain.discard(test, x -> x % 2 != 0));
+
+	}
+
+	@Test
+	public void discardNeitherFirstNorLast() {
+		List<Integer> expected = Arrays.asList(1, 3, 5);
+		List<Integer> test = Arrays.asList(1, 2, 3, 4, 5);
+		Assert.assertEquals(expected, Strain.discard(test, x -> x % 2 == 0));
+	}
+
+	@Test
+	public void discardStrings() {
+		List<String> words = Arrays
+				.asList("apple zebra banana zombies cherimoya zelot".split(" "));
+		List<String> expected = Arrays.asList("apple", "banana", "cherimoya");
+		Assert.assertEquals(expected,
+				Strain.discard(words, x -> x.startsWith("z")));
+	}
+
+	@Test
+	public void discardArrays() {
+		List<List<Integer>> actual = Arrays.asList(
+				Arrays.asList(1, 2, 3),
+				Arrays.asList(5, 5, 5),
+				Arrays.asList(5, 1, 2),
+				Arrays.asList(2, 1, 2),
+				Arrays.asList(1, 5, 2),
+				Arrays.asList(2, 2, 1),
+				Arrays.asList(1, 2, 5));
+		List<List<Integer>> expected = Arrays.asList(
+				Arrays.asList(1, 2, 3),
+				Arrays.asList(2, 1, 2),
+				Arrays.asList(2, 2, 1));
+		Assert.assertEquals(expected,
+				Strain.discard(actual, col -> col.contains(5)));
+	}
+}