stringbuilder Scala drop duplicate chars - scala

Question

class Buffer(s: String) {
import scala.collection.mutable.StringBuilder
import scala.io.StdIn
private var buffer: StringBuilder = new StringBuilder(s)
private var cursor: Int = 0 // cursor is in between characters
private var marker: Int = 0 // marker is in between characters
private var paste: String = ""
private def end: Int = buffer.length // the end of the line
private def lwr: Int = Math.min(marker, cursor)
private def upr: Int = Math.max(marker, cursor)
/*
* Accessor methods to return aspects of the state
*/
def getCursor: Int = cursor
def getMarker: Int = marker
def getString: String = buffer.toString
def getPaste: String = paste
/**
* Delete Duplicate characters. Within the defined region, for each character,
* if it occurs once then keep it, but if it occurs multiple times then keep
* only the first occurrence. The characters to the left and right of the
* defined region remain unchanged, but within the defined region the duplicates
* are removed. This operation does not affect the paste buffer. The cursor is
* placed finally at the lower end of the defined region and the marker is placed
* finally at the upper end of the (probably reduced) defined region. For example:
*
* m i s s i s s i p p i marker = 1
* ^ ^ cursor = 10
*
* Then perform sc('a', 'X')
*
* m i s p i marker = 1
* ^ ^ cursor = 4
*/
def dd()
{
var droppedchars: Int = 0;
for (x <- lwr until upr)
{
var c = buffer.charAt(x)
for (i <- lwr until upr)
{
if (buffer.charAt(i) == c)
{
buffer.deleteCharAt(i)
droppedchars += 1
}
}
marker = lwr
cursor = upr - droppedchars
}
}
Need some help with this one too, doesn't appear to work
function needs to drop any duplicate chars it finds, move the marker back to the start of the new defined region and the cursor to the end of the new defined region, not asking for somebody to write this for me just guide me in the right direction

Answer 1

Why not just:
scala> "mississippi".distinct
res22: String = misp

Answer 2

What you're trying to do takes O(n^2) that is not very good from performance perspective...
Imo, a better one solution is use only one loop over the buffer and within it an each character c you should check with a set of characters (declared outside the for-loop):
val chars = scala.collection.mutable.Set[Char]()
...
for (x <- lwr until upr) {
var c = buffer.charAt(x)
if (chars contains c) buffer.deleteCharAt(x) else chars += c
}
cursor = marker + chars.size