ContainsDuplicate.java

import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import java.util.HashSet;
import java.util.Set;

/**
 * Given an array of integers, find if the array contains any duplicates. Your function should return true if any value
 * appears at least twice in the array, and it should return false if every element is distinct.
 * <p>
 * Tags: Array, Hash Table
 * Similar Problems: (E) Contains Duplicate II, (M) Contains Duplicate III
 */
public class ContainsDuplicate {

    private ContainsDuplicate cd;

    public boolean containsDuplicate(int[] nums) {
        if (nums == null || nums.length <= 1) return false;
        Set<Integer> set = new HashSet<>(nums.length);
        for (int n : nums) {
            if (!set.add(n)) return true;
        }
        return false;
    }

    @Before
    public void setUp() {
        cd = new ContainsDuplicate();
    }

    @Test
    public void testEdgeCases() {
        Assert.assertFalse(cd.containsDuplicate(null));
        Assert.assertFalse(cd.containsDuplicate(new int[]{}));
        Assert.assertFalse(cd.containsDuplicate(new int[]{1}));
    }

    @Test
    public void testExamples() {
        Assert.assertFalse(cd.containsDuplicate(new int[]{1, 2}));
        Assert.assertTrue(cd.containsDuplicate(new int[]{1, 1}));
    }

    @After
    public void tearDown() {
        cd = null;
    }

}