Counting Sort (Java Version)

CountingSorter.java

public class CountingSorter implements Sorter {
	private final int maxValue;

	public CountingSorter(int maxValue) {
		this.maxValue = maxValue;
	}

	@Override
	public int[] sort(int[] values) {
		int[] counts = new int[maxValue + 1];
		for (int i = 0; i < values.length; i++) {
			counts[values[i]]++;
		}

		int total = 0;
		for (int i = 0; i <= maxValue; i++) {
			int count = counts[i];
			counts[i] = total;
			total += count;
		}

		int[] sortedValues = new int[values.length];
		for (int i = 0; i < values.length; i++) {
			sortedValues[counts[values[i]]] = values[i];
			counts[values[i]]++;
		}
		return sortedValues;
	}
}

CountingSorterTest.java

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

import org.junit.Test;

public class CountingSorterTest {
	@Test
	public void testSort() {
		int maxScore = 100;
		int[] expectedSortedScores = { 60, 80, 80, 100 };
		int[] scores = { 80, 80, 60, 100 };

		Sorter sorter = new CountingSorter(maxScore);
		int[] sortedScores = sorter.sort(scores);

		assertThat(sortedScores, is(expectedSortedScores));
	}
}

Sorter.java

public interface Sorter {
	int[] sort(int[] values);
}