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

class Solution{
    public int[] twoSum(int[] nums, int target){
        Map<Integer, Integer> map = new HashMap<>();

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

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

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

        throw new IllegalArgumentException("No two Sum solution.");
    }
}