--- a/pre_solution3/postfix2.scala	Mon Nov 08 00:17:50 2021 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,100 +0,0 @@
-// Shunting Yard Algorithm 
-// including Associativity for Operators 
-// =====================================
-
-object CW8b {
-
-// type of tokens
-type Toks = List[String]
-
-// helper function for splitting strings into tokens
-def split(s: String) : Toks = s.split(" ").toList
-
-// left- and right-associativity
-abstract class Assoc
-case object LA extends Assoc
-case object RA extends Assoc
-
-// power is right-associative,
-// everything else is left-associative
-def assoc(s: String) : Assoc = s match {
-  case "^" => RA
-  case _ => LA
-}
-
-// the precedences of the operators
-val precs = Map("+" -> 1,
-  		 "-" -> 1,
-		 "*" -> 2,
-		 "/" -> 2,
-                 "^" -> 4)
-
-// the operations in the basic version of the algorithm
-val ops = List("+", "-", "*", "/", "^")
-
-// (8) Implement the extended version of the shunting yard algorithm.
-// This version should properly account for the fact that the power 
-// operation is right-associative. Apart from the extension to include
-// the power operation, you can make the same assumptions as in 
-// basic version.
-
-def is_op(op: String) : Boolean = ops.contains(op)
-
-def prec(op1: String, op2: String) : Boolean = assoc(op1) match {
-  case LA => precs(op1) <= precs(op2)
-  case RA => precs(op1) < precs(op2)
-}
-
-def syard(toks: Toks, st: Toks = Nil, out: Toks = Nil) : Toks = (toks, st, out) match {
-  case (Nil, _, _) => out.reverse ::: st
-  case (num::in, st, out) if (num.forall(_.isDigit)) => 
-    syard(in, st, num :: out)
-  case (op1::in, op2::st, out) if (is_op(op1) && is_op(op2) && prec(op1, op2)) =>
-    syard(op1::in, st, op2 :: out) 
-  case (op1::in, st, out) if (is_op(op1)) => syard(in, op1::st, out)
-  case ("("::in, st, out) => syard(in, "("::st, out)
-  case (")"::in, op2::st, out) =>
-    if (op2 == "(") syard(in, st, out) else syard(")"::in, st, op2 :: out)
-  case (in, st, out) => {
-    println(s"in: ${in}   st: ${st}   out: ${out.reverse}")
-    Nil
-  }  
-} 
-
-def op_comp(s: String, n1: Int, n2: Int) = s match {
-  case "+" => n2 + n1
-  case "-" => n2 - n1
-  case "*" => n2 * n1
-  case "/" => n2 / n1
-  case "^" => BigInt(n2).pow(n1).toInt
-} 
-
-def compute(toks: Toks, st: List[Int] = Nil) : Int = (toks, st) match {
-  case (Nil, st) => st.head
-  case (op::in, n1::n2::st) if (is_op(op)) => compute(in, op_comp(op, n1, n2)::st)
-  case (num::in, st) => compute(in, num.toInt::st)  
-}
-
-
-
-
-//compute(syard(split("3 + 4 * ( 2 - 1 )")))   // 7
-//compute(syard(split("10 + 12 * 33")))       // 406
-//compute(syard(split("( 5 + 7 ) * 2")))      // 24
-//compute(syard(split("5 + 7 / 2")))          // 8
-//compute(syard(split("5 * 7 / 2")))          // 17
-//compute(syard(split("9 + 24 / ( 7 - 3 )"))) // 15
-
-//compute(syard(split("4 ^ 3 ^ 2")))      // 262144
-//compute(syard(split("4 ^ ( 3 ^ 2 )")))  // 262144
-//compute(syard(split("( 4 ^ 3 ) ^ 2")))  // 4096
-//compute(syard(split("( 3 + 1 ) ^ 2 ^ 3")))   // 65536
-
-//syard(split("3 + 4 * 8 / ( 5 - 1 ) ^ 2 ^ 3"))  // 3 4 8 * 5 1 - 2 3 ^ ^ / +
-//compute(syard(split("3 + 4 * 8 / ( 5 - 1 ) ^ 2 ^ 3"))) // 3
-
-//compute(syard(split("( 3 + 1 ) ^ 2 ^ 3")))   // 65536
-
-
-
-}