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;
    }
}