scala coding to do the Huffman decoding, but wrong result - scala

Question

abstract class CodeTree
case class Fork(left: CodeTree, right: CodeTree, chars: List[Char], weight: Int) extends CodeTree
case class Leaf(char: Char, weight: Int) extends CodeTree
type Bit = Int
def decode(tree: CodeTree, bits: List[Bit]): List[Char] = {
if(!bits.isEmpty) {
bits.head match {
case 0 => tree match {
case Fork(l, r, _, _) => decode(l, bits.tail)
case Leaf(_, _) => chars(tree) ::: decode(frenchCode, bits.tail)
}
case 1 => tree match {
case Fork(l, r, _, _) => decode(r, bits.tail)
case Leaf(_, _) => chars(tree) ::: decode(frenchCode, bits.tail)
}
}
}
else Nil
}
val frenchCode: CodeTree = Fork(Fork(Fork(Leaf('s',121895),Fork(Leaf('d',56269),Fork(Fork(Fork(Leaf('x',5928),Leaf('j',8351),List('x','j'),14279),Leaf('f',16351),List('x','j','f'),30630),Fork(Fork(Fork(Fork(Leaf('z',2093),Fork(Leaf('k',745),Leaf('w',1747),List('k','w'),2492),List('z','k','w'),4585),Leaf('y',4725),List('z','k','w','y'),9310),Leaf('h',11298),List('z','k','w','y','h'),20608),Leaf('q',20889),List('z','k','w','y','h','q'),41497),List('x','j','f','z','k','w','y','h','q'),72127),List('d','x','j','f','z','k','w','y','h','q'),128396),List('s','d','x','j','f','z','k','w','y','h','q'),250291),Fork(Fork(Leaf('o',82762),Leaf('l',83668),List('o','l'),166430),Fork(Fork(Leaf('m',45521),Leaf('p',46335),List('m','p'),91856),Leaf('u',96785),List('m','p','u'),188641),List('o','l','m','p','u'),355071),List('s','d','x','j','f','z','k','w','y','h','q','o','l','m','p','u'),605362),Fork(Fork(Fork(Leaf('r',100500),Fork(Leaf('c',50003),Fork(Leaf('v',24975),Fork(Leaf('g',13288),Leaf('b',13822),List('g','b'),27110),List('v','g','b'),52085),List('c','v','g','b'),102088),List('r','c','v','g','b'),202588),Fork(Leaf('n',108812),Leaf('t',111103),List('n','t'),219915),List('r','c','v','g','b','n','t'),422503),Fork(Leaf('e',225947),Fork(Leaf('i',115465),Leaf('a',117110),List('i','a'),232575),List('e','i','a'),458522),List('r','c','v','g','b','n','t','e','i','a'),881025),List('s','d','x','j','f','z','k','w','y','h','q','o','l','m','p','u','r','c','v','g','b','n','t','e','i','a'),1486387)
val secret: List[Bit] = List(0,0,1,1,1,0,1,0,1,1,1,0,0,1,1,0,1,0,0,1,1,0,1,0,1,1,0,0,1,1,1,1,1,0,1,0,1,1,0,0,0,0,1,0,1,1,1,0,0,1,0,0,1,0,0,0,1,0,0,0,1,0,1)
def decodedSecret: List[Char] = decode(frenchCode, secret)ode here
I am new to scala, and learning the pattern matching now, I want to do the huffman decoding, now I could get a list, but it is the wrong answer, hope someone could find the mistake.

Answer 1

There are several issues with your code.
You do not want to consume a bit when you hit a leaf. A character of the leaf should also be added if there is no bit in your code.
In the decode methode you do not want to reference frenchCode, but code instead that is given as a parameter.
You can access the char of the leaf via pattern matching, i.e. case Leaf(codeChar, _) => ...
Btw. your code will be way cleaner if you start matching on the tree. Only if it matches to a fork you look at the head of your bit list.
Hope that helps. ;)