Solution for https://dzone.com/articles/java-code-challenge-node-degrees

NodeDegrees.java

package software.schwering.javacodechallenge;

import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.TreeMap;
import java.util.stream.Stream;

public class NodeDegrees extends TreeMap<Integer, Long> {
	
	private static final long serialVersionUID = 1L;

	public NodeDegrees(Path inputFile) throws IOException {
		this(Files.lines(inputFile).skip(1));
	}

	public NodeDegrees(Stream<String> input) {
		putAll(input.map(s -> s.split(" "))
					.flatMap(s -> Stream.of(s))
					.collect(groupingBy(Integer::new, counting())));
	}

	public static void main(String... args) throws IOException {
		new NodeDegrees(Paths.get(args[0]))
			.forEach((node, degree)-> System.out.format("Node %d has a degree of %d\n", node, degree));
	}

}

NodeDegreesTest.java

package software.schwering.javacodechallenge;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.*;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.util.stream.Stream;

import org.hamcrest.BaseMatcher;
import org.hamcrest.Description;
import org.hamcrest.Matcher;
import org.junit.Test;

public class NodeDegreesTest {

	@Test
	public void noDegreesForEmptyInput() {
		Stream<String> input = Stream.of();

		NodeDegrees nodeDegrees = new NodeDegrees(input);

		assertThat(nodeDegrees.size(), is(0));
	}

	@Test
	public void twoDegreesOf1forOneEdge() {
		Stream<String> input = Stream.of("1 2");

		NodeDegrees nodeDegrees = new NodeDegrees(input);

		assertThat(nodeDegrees.size(), is(2));
		assertThat(nodeDegrees.get(1), hasDegreeOf(1));
		assertThat(nodeDegrees.get(2), hasDegreeOf(1));
	}

	@Test
	public void incomingAndOutgoringEdgeIsCounted() {
		Stream<String> input = Stream.of("1 2", "2 3");

		NodeDegrees nodeDegrees = new NodeDegrees(input);

		assertThat(nodeDegrees.size(), is(3));
		assertThat(nodeDegrees.get(1), hasDegreeOf(1));
		assertThat(nodeDegrees.get(2), hasDegreeOf(2));
		assertThat(nodeDegrees.get(3), hasDegreeOf(1));
	}

	@Test
	public void example() {
		Stream<String> input = Stream.of("1 2", "1 3", "2 3", "1 4", "3 4", "1 5", "2 5", "1 6", "2 6", "3 6", "3 7",
				"5 7", "6 7", "3 8", "4 8", "6 8", "7 8", "2 9", "5 9", "6 9", "2 10", "9 10", "6 11", "7 11", "8 11",
				"9 11", "10 11", "1 12", "6 12", "7 12", "8 12", "11 12", "6 13", "7 13", "9 13", "10 13", "11 13",
				"5 14", "8 14", "12 14", "13 14", "1 15", "2 15", "5 15", "9 15", "10 15", "11 15", "12 15", "13 15",
				"1 16", "2 16", "5 16", "6 16", "11 16", "12 16", "13 16", "14 16", "15 16");

		NodeDegrees nodeDegrees = new NodeDegrees(input);

		assertThat(nodeDegrees.size(), is(16));
		assertThat(nodeDegrees.get(1), hasDegreeOf(8));
		assertThat(nodeDegrees.get(2), hasDegreeOf(8));
		assertThat(nodeDegrees.get(3), hasDegreeOf(6));
		assertThat(nodeDegrees.get(4), hasDegreeOf(3));
		assertThat(nodeDegrees.get(5), hasDegreeOf(7));
		assertThat(nodeDegrees.get(6), hasDegreeOf(10));
		assertThat(nodeDegrees.get(7), hasDegreeOf(7));
		assertThat(nodeDegrees.get(8), hasDegreeOf(7));
		assertThat(nodeDegrees.get(9), hasDegreeOf(7));
		assertThat(nodeDegrees.get(10), hasDegreeOf(5));
		assertThat(nodeDegrees.get(11), hasDegreeOf(9));
		assertThat(nodeDegrees.get(12), hasDegreeOf(8));
		assertThat(nodeDegrees.get(13), hasDegreeOf(8));
		assertThat(nodeDegrees.get(14), hasDegreeOf(5));
		assertThat(nodeDegrees.get(15), hasDegreeOf(9));
		assertThat(nodeDegrees.get(16), hasDegreeOf(9));
	}

	@Test
	public void exampleStringFormat() throws IOException {
		ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
		PrintStream out = new PrintStream(byteStream);
		System.setOut(out);

		NodeDegrees.main("in.txt");

		assertEquals("Node 1 has a degree of 8\n" + "Node 2 has a degree of 8\n" + "Node 3 has a degree of 6\n"
				+ "Node 4 has a degree of 3\n" + "Node 5 has a degree of 7\n" + "Node 6 has a degree of 10\n"
				+ "Node 7 has a degree of 7\n" + "Node 8 has a degree of 7\n" + "Node 9 has a degree of 7\n"
				+ "Node 10 has a degree of 5\n" + "Node 11 has a degree of 9\n" + "Node 12 has a degree of 8\n"
				+ "Node 13 has a degree of 8\n" + "Node 14 has a degree of 5\n" + "Node 15 has a degree of 9\n"
				+ "Node 16 has a degree of 9\n", byteStream.toString());
	}

	private static Matcher<Long> hasDegreeOf(long degree) {
		return new BaseMatcher<Long>() {

			@Override
			public boolean matches(Object item) {
				return Long.valueOf(degree).equals(item);
			}

			@Override
			public void describeTo(Description description) {
				description.appendText("the node should have a degree of").appendValue(degree);
			}
		};
	}

}