diff -r 19b75e899d37 -r 9c03b5e89a2a assignment2021scala/core3/postfix.scala --- a/assignment2021scala/core3/postfix.scala Fri Apr 26 17:29:30 2024 +0100 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,81 +0,0 @@ -// Shunting Yard Algorithm -// by Edsger Dijkstra -// ======================== - -object C3a { - -// type of tokens -type Toks = List[String] - -// the operations in the basic version of the algorithm -val ops = List("+", "-", "*", "/") - -// the precedences of the operators -val precs = Map("+" -> 1, - "-" -> 1, - "*" -> 2, - "/" -> 2) - -// helper function for splitting strings into tokens -def split(s: String) : Toks = s.split(" ").toList - - -// (1) Implement below the shunting yard algorithm. The most -// convenient way to this in Scala is to implement a recursive -// function and to heavily use pattern matching. The function syard -// takes some input tokens as first argument. The second and third -// arguments represent the stack and the output of the shunting yard -// algorithm. -// -// In the marking, you can assume the function is called only with -// an empty stack and an empty output list. You can also assume the -// input os only properly formatted (infix) arithmetic expressions -// (all parentheses will be well-nested, the input only contains -// operators and numbers). - -// You can implement any additional helper function you need. I found -// it helpful to implement two auxiliary functions for the pattern matching: -// - -def is_op(op: String) : Boolean = ??? -def prec(op1: String, op2: String) : Boolean = ??? - - -def syard(toks: Toks, st: Toks = Nil, out: Toks = Nil) : Toks = ??? - - -// test cases -//syard(split("3 + 4 * ( 2 - 1 )")) // 3 4 2 1 - * + -//syard(split("10 + 12 * 33")) // 10 12 33 * + -//syard(split("( 5 + 7 ) * 2")) // 5 7 + 2 * -//syard(split("5 + 7 / 2")) // 5 7 2 / + -//syard(split("5 * 7 / 2")) // 5 7 * 2 / -//syard(split("9 + 24 / ( 7 - 3 )")) // 9 24 7 3 - / + - -//syard(split("3 + 4 + 5")) // 3 4 + 5 + -//syard(split("( ( 3 + 4 ) + 5 )")) // 3 4 + 5 + -//syard(split("( 3 + ( 4 + 5 ) )")) // 3 4 5 + + -//syard(split("( ( ( 3 ) ) + ( ( 4 + ( 5 ) ) ) )")) // 3 4 5 + + - - -// (2) Implement a compute function that evaluates an input list -// in postfix notation. This function takes a list of tokens -// and a stack as argumenta. The function should produce the -// result as an integer using the stack. You can assume -// this function will be only called with proper postfix -// expressions. - -def compute(toks: Toks, st: List[Int] = Nil) : Int = ??? - - -// test cases -// 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 - -} - -