/* 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. */ public String notReplace(String str) { if(str.equals("is")) return "is not"; StringBuilder result = new StringBuilder(); int i = 0; if(str.length() >= 3 && str.substring(0,2).equals("is") && !Character.isLetter(str.charAt(2))) { result.append("is not"); i = 2; } while(i < str.length()) { if(!Character.isLetter(str.charAt(i))) { result.append(str.charAt(i)); i++; } else if(i >= 1 && i <= str.length()-3 && !Character.isLetter(str.charAt(i-1)) && str.substring(i,i+2).equals("is") && !Character.isLetter(str.charAt(i+2))) { result.append("is not"); i += 2; } else if(i >= 1 && !Character.isLetter(str.charAt(i-1)) && str.substring(i).equals("is")) { result.append("is not"); i += 2; } else { result.append(str.charAt(i)); i++; } } return result.toString(); }