Two Sum

 

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

public class TwoSum {

    @Test
    public void test() {

        int[] array = new int[]{2, 7, 11, 15};
        int target = 9;
        int[] result = new int[]{0, 1};
        Assertions.assertTrue(Arrays.equals(twoSum(array, target), result));

        array = new int[]{3, 2, 4};
        target = 6;
        result = new int[]{1, 2};
        Assertions.assertTrue(Arrays.equals(twoSum(array, target), result));

        array = new int[]{3, 3};
        target = 6;
        result = new int[]{0, 1};
        Assertions.assertTrue(Arrays.equals(twoSum(array, target), result));
    }

    public int[] twoSum(int[] array, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < array.length; i++) {
            if (map.containsKey(array[i])) {
                return new int[]{map.get(array[i]), i};
            }
            map.put(target - array[i], i);
        }
        return null;
    }
}

Valid Anagram

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.Arrays;

public class ValidAnagram {

    @Test
    public void test() {
        String s = "anagram";
        String t = "nagaram";
        Assertions.assertTrue(isAnagram(s, t));
        Assertions.assertTrue(isAnagramWithKey(s, t));

        String a = "rat";
        String b = "cat";
        Assertions.assertFalse(isAnagram(a, b));
        Assertions.assertFalse(isAnagramWithKey(a, b));

    }

    public boolean isAnagram(String s, String t) {
        int[] array = new int[128];
        for (char c : s.toCharArray()) {
            array[c]++;
        }
        for (char c : t.toCharArray()) {
            array[c]--;
        }
        for (int a : array) {
            if (a != 0) {
                return false;
            }
        }
        return true;
    }

    public boolean isAnagramWithKey(String s, String t) {
        return key(s).equals(key(t));
    }

    public String key(String s) {
        int[] array = new int[128];
        for (char c : s.toCharArray()) {
            array[c]++;
        }
        return Arrays.toString(array);
    }
}

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;
    }
}