Two Sum

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        if (nums == null) {
    		throw new IllegalArgumentException("");
    	}
    	int [] res = new int[2];
    	if (nums.length < 2) {
    		return res;
    	}
    	Map<Integer, Integer> map = new HashMap<>();
    	for (int i = 0; i < nums.length; i++) {
    		if (map.containsKey(nums[i])) {
    			int idxa = map.get(nums[i]);
    			res[0] = idxa;
    			res[1] = i;
    		} else {
    			map.put(target - nums[i], i);
    		}
    	}
    	return res;
    }
}