TwoSum.java

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