Java > String-3 > notReplace (CodingBat Solution)

Problem:

Given a string, return a string where every appearance of the lowercase word "is" has been replaced with "is not". The word "is" should not be immediately preceeded or followed by a letter -- so for example the "is" in "this" does not count. (Note: Character.isLetter(char) tests if a char is a letter.)

notReplace("is test") → "is not test"
notReplace("is-is") → "is not-is not"
notReplace("This is right") → "This is not right"

Solution:

public String notReplace(String str) {
  String result = "";
  int len = str.length();
  
  for(int i = 0; i < len; i++){
    if(i-1 >= 0 && Character.isLetter(str.charAt(i-1))
    || i+2 < len && Character.isLetter(str.charAt(i+2))) {
      result += str.charAt(i);
    }
    else if(i+1 < len && str.substring(i, i+2).equals("is")) {
      result += "is not";
      i++;
    }
    else result += str.charAt(i);
  }
  return result;
}