017.Letter Combinations of a Phone Number

Posted on | In

Solution 1: accepted 4ms

Pretty massy, need to be improved. 

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public List<String> letterCombinations(String digits) {
  List<String> result = new ArrayList<>();
  String[] map = {"", "", "abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
  for (int i = 0; i < digits.length(); i++) {
    char digit = digits.charAt(i);
    if (digit == '0' || digit == '1') 
      return new ArrayList<>();
    result = appendAll(result, map[digit - '0']);  
  }
  return result;
}
public List<String> appendAll(List<String> result, String chars) {
  List<String> update = new ArrayList<>();
  Iterator<String> it = result.iterator();
  
  if (result.size() == 0) {
    for (int i = 0; i < chars.length(); i++) {
      update.add(chars.charAt(i) + "");
    }
  } else {
    while(it.hasNext()) {
      String current = it.next();
      for (int i = 0; i < chars.length(); i++) {
        update.add(current + chars.charAt(i));
      }
    }
  }
  return update;
}