comefrom: <gouthampradhan>backtracking_LetterCasePermutation_1.java
code: private void backtrack(String s, List<String> result, int i, String r) {
      if (i == s.length()) {
        result.add(r);
      } else {
        if (Character.isAlphabetic(s.charAt(i))) {
          backtrack(s, result, i + 1, r + s.charAt(i));
          if (Character.isLowerCase(s.charAt(i))) {
            backtrack(s, result, i + 1, r + Character.toUpperCase(s.charAt(i)));
          } else {
            backtrack(s, result, i + 1, r + Character.toLowerCase(s.charAt(i)));
          }
        } else {
          backtrack(s, result, i + 1, r + s.charAt(i));
        }
      }
    }
masked: private void sample_funcname ( String s , List < String > result , int i , String r ) {
    if ( i == s . length ( ) ) {
      result . add ( r ) ;
    }
    else {
      if ( Character . isAlphabetic ( s . charAt ( i ) ) ) {
        backtrack ( s , result , i + 1 , r + s . charAt ( i ) ) ;
        if ( Character . isLowerCase ( s . charAt ( i ) ) ) {
          backtrack ( s , result , i + 1 , r + Character . toUpperCase ( s . charAt ( i ) ) ) ;
        }
        else {
          backtrack ( s , result , i + 1 , r + Character . toLowerCase ( s . charAt ( i ) ) ) ;
        }
      }
      else {
        backtrack ( s , result , i + 1 , r + s . charAt ( i ) ) ;
      }
    }
  }
  