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<Integer, Integer> 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();

}

}