// Time: O(n)
// Space: O(n)
class Solution {
public int[] twoSum(int[] nums, int target) {
Map lookup = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
if (lookup.containsKey(target - nums[i])) {
return new int[] { lookup.get(target - nums[i]), i };
}
lookup.put(nums[i], i);
}
return null;
}
}