04_TwoSum.java

// Problem: Two Sum
// Author: Atabul (codeByunique)

import java.util.HashMap;

class TwoSum {
    public static void main(String[] args) {
        int[] nums = {2, 7, 11, 15};
        int target = 9;

        int[] result = findTwoSum(nums, target);
        if (result.length == 2) {
            System.out.println("Indices: [" + result[0] + ", " + result[1] + "]");
        } else {
            System.out.println("No valid pair found.");
        }
    }

    public static int[] findTwoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();

        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];

            if (map.containsKey(complement)) {
                return new int[]{map.get(complement), i};
            }

            map.put(nums[i], i);
        }

        return new int[]{}; // no pair found
    }
}