Contains Duplicate

 

import org.junit.jupiter.api.Test;

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

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class ContainsDuplicate {

    @Test
    public void test() {
        int[] a = {1, 2, 3, 1};
        assertTrue(containsDuplicateWithSet(a));
        assertTrue(containsDuplicateWithSort(a));
        assertTrue(containsDuplicateWithStream(a));

        int[] b = {1, 2, 3, 4};
        assertFalse(containsDuplicateWithSet(b));
        assertFalse(containsDuplicateWithSort(b));
        assertFalse(containsDuplicateWithStream(b));

        int[] c = {1, 1, 1, 3, 3, 4, 3, 2, 4, 2};
        assertTrue(containsDuplicateWithSet(c));
        assertTrue(containsDuplicateWithSort(c));
        assertTrue(containsDuplicateWithStream(c));
    }

    public boolean containsDuplicateWithSet(int[] array) {
        Set<Integer> set = new HashSet<>();
        for (int num : array) {
            if (!set.add(num)) {
                return true;
            }
        }
        return false;
    }

    public boolean containsDuplicateWithSort(int[] array) {
        Arrays.sort(array);
        for (int i = 1; i < array.length; i++) {
            if (array[i - 1] == array[i]) {
                return true;
            }
        }
        return false;
    }

    public boolean containsDuplicateWithStream(int[] array){
        return Arrays.stream(array).distinct().count()!=array.length;
    }
}