import java.util.HashMap;
import java.util.Map;
public class TwoSum {
public int[] twoSum(int[] nums, int target) {
if (nums == null || nums.length < 2) {
throw new IllegalArgumentException();
}
Map map = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
if (map.containsKey(target - nums[i])) {
return new int[] {map.get(target - nums[i]), i};
}
map.put(nums[i], i);
}
throw new IllegalArgumentException();
}
}