DZone :: Code Challenge Series: Substring Search

StringFinder.scala

object StringFinder {
  /**
   * Finds the first occurrence of a substring (`query`) within a `text`.
   * @param text - the text to search in.
   * @param query - the substring to find in `text`.
   * @param pos - position in text to start searching from.
   */
  def find(text: String, query: String)(pos: Int): Unit = {
    /*
     * make sure `pos` hasn't gone out
     * of range of what can be queried within `text`.
     */
    if (pos >= 0 && pos <= text.length - query.length) {
      /*
       * make a substring based on extracting the characters
       * from `pos` to `pos + query.length` exclusive.
       */
      val subText =
        (for (j <- pos until pos + query.length)
          yield text.charAt(j)).mkString("")

      // compare the extracted sub-text with `query`.
      if (subText == query)
        // let the user know `query` has been found and where.
        println(s"""First occurrence of "$query" found at $pos""")
      else {
        /*
         * so it wasn't found now, try searching
         * from the next character in `text`.
         */
        find(text, query)(pos + 1)
      }
    } else {
      // `query` wasn't found in `text` at all.
      println(s""""$query" doesn't exist anywhere in the text.""")
    }
  }
}