two_sum

.java

package com.yambacode.sandbox;

import java.util.Arrays;
import java.util.stream.IntStream;

public class Main {

    public static Integer[] solve_1(int target, Integer... nums) {
        for (int i = 0; i < nums.length - 1; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[i] + nums[j] == target) {
                    return new Integer[]{i, j};
                }
            }
        }
        return new Integer[]{};
    }

    public static Integer[] solve_2(int target, Integer... nums) {
        return IntStream.range(0, nums.length - 1)
                .mapToObj(i ->
                        IntStream.range(i + 1, nums.length)
                                .mapToObj(j -> ((nums[i] + nums[j]) == target) ? new Integer[]{i, j} : new Integer[]{})
                                .reduce((a1, a2) -> (a1.length > a2.length) ? a1 : a2).get())
                .findFirst()
                .get();
    }

    public static void main(String[] args) {
        System.out.println("1.Answer is: " + Arrays.deepToString(solve_1(9, 2, 7, 11, 15)));
        System.out.println("1.Answer is: " + Arrays.deepToString(solve_2(9, 2, 7, 11, 15)));
        System.out.println("2.Answer is: " + Arrays.deepToString(solve_1(6, 3, 2, 4)));
        System.out.println("2.Answer is: " + Arrays.deepToString(solve_2(6, 3, 2, 4)));
        System.out.println("3.Answer is: " + Arrays.deepToString(solve_1(6, 3, 3)));
        System.out.println("3.Answer is: " + Arrays.deepToString(solve_2(6, 3, 3)));
    }
}