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