code: public static String insert(final String str, final String given, final int begin, final int end) {
      if (begin < 1 || end > str.length() || end < begin) { return str; }
      return str.substring(0, begin - 1) + given + str.substring(end);
    }
docs: replace [bigen,end] [1...end] with givenStr
  可以使用StringBuilder的replace方法替换该方法
  
  @param str a {@link java.lang.String} object.
  @param begin a int.
  @param end a int.
  @param given a {@link java.lang.String} object.
  @return a {@link java.lang.String} object.