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TwoSum.java

public class TwoSum {
  // Return indices that sum to target
  public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map =
        new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
      int diff = target - nums[i];
      if (map.containsKey(diff))
        return new int[] { map.get(diff), i };
      map.put(nums[i], i);
    }
    return new int[] {};
  }
}

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