Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

public int[] twoSum(int[] nums, int target) {
            int[] answer = new int[2];
            HashMap<Integer, Integer> map = new HashMap<>();
            for (int i = 0; i < nums.length; ++i){
                map.put(nums[i], i);
            }
            for (int i = 0; i < nums.length; ++i){
                int b = target - nums[i];
                if (map.containsKey(b) && i != map.get(b))
                    return new int[]{i, map.get(b)};
             }
             return answer;
        }