Start with two arrays of strings, A and B, each with its elements in alphabetical order and without duplicates. Return a new array containing the first N elements from the two arrays. The result array should be in alphabetical order and without duplicates. A and B will both have a length which is N or more. The best "linear" solution makes a single pass over A and B, taking advantage of the fact that they are in alphabetical order, copying elements directly to the new array.
mergeTwo(["a", "c", "z"], ["b", "f", "z"], 3) → ["a", "b", "c"]
mergeTwo(["a", "c", "z"], ["c", "f", "z"], 3) → ["a", "c", "f"]
mergeTwo(["f", "g", "z"], ["c", "f", "g"], 3) → ["c", "f", "g"]

Solution:

public String[] mergeTwo(String[] a, String[] b, int n) {
  String[] s = new String[n];
  int indexA = 0;
  int indexB = 0;
  int resultIndex = 0;
  while(resultIndex < n) {
    if(a[indexA].compareTo(b[indexB]) < 0) {
      s[resultIndex++] = a[indexA++];
    }else if(a[indexA].compareTo(b[indexB]) > 0) {
      s[resultIndex++] = b[indexB++];
    }else { // identical string, increment both.
      s[resultIndex++] = b[indexB++];
      indexA++;
    }
  }
  return s;
}