Converter notação infix em postfix

private var stack = mutableListOf<String>()
private var queue = mutableListOf<String>()
private var expressionList = mutableListOf<String>()

fun main() {
    parseExpression()
}

fun parseExpression() {
    "5*8*(2+9)+(7-5+8-9*(5*5)+5)".forEach {
        expressionList.add(it.toString())
    }
    print(" : ")
    expressionList.forEach {
        print(it)
    }
    println()
}

private fun getPostFixEx() {
    //  expressionList
    expressionList.forEach {
        when {
            //      PUSH
            it == "(" -> push(it)

            //      POP
            it == ")" -> {
                if (expressionList.contains("(")) {
                    pop()
                }
            }

            //   ,    
            Regex("[\\d]").containsMatchIn(it) -> addQueue(it)

            //   +  -
            Regex("[+-]").containsMatchIn(it) ->
                /* ,         ,
                *   PUSH */
                if (stack.isEmpty() || stack.last() == "(") push(it)
                /* ,       
                * ,   POP,  PUSH */
                else if (stack.last().contains(Regex("[/*]"))) {
                    pop()
                    push(it)
                }
                //    PUSH
                else {
                    addQueue(stack.last())
                    stack[stack.lastIndex] = it
                }

            //   *  /
            Regex("[*/]").containsMatchIn(it) -> {
                /* ,         ,
                *   POP */
                if (stack.isNotEmpty() && (stack.last() == "*" || stack.last() == "/")) {
                    pop()
                }
                //   PUSH
                push(it)
            }
        }
    }
    //     ,       
    if (stack.isNotEmpty()) {
        for (i in stack.lastIndex downTo 0) {
            if (stack[i] != "(") {
                addQueue(stack[i])
            }
        }
    }
    print(" : ")
    queue.forEach {
            print(it)
    }
    println()

}

private fun pop() {
    //         ,     
    Loop@ for (i in stack.lastIndex downTo 0) {
        if (stack[i] == "(") {
            stack[i] = " "
            break@Loop
        }
        addQueue(stack[i])
        stack[i] = " "
    }
    stack.removeIf { it == " " }
}

private fun addQueue(item: String) {
    queue.add(item)
}

private fun push(item: String) {
    stack.add(item)
}

private fun calcPostFix() {
    //   
    val stack = mutableListOf<Int>()
    //    
    for (item in queue) {
        when {
            //    - ,    
            Regex("[\\d]").containsMatchIn(item) -> {
                stack.add(item.toInt())
            }
            /*    + ,    
                */
            item == "+" -> {
                stack[stack.lastIndex - 1] = stack[stack.lastIndex - 1] + stack.last()
                stack.removeAt(stack.lastIndex)
            }
            /*    * ,    
                */
            item == "*" -> {
                stack[stack.lastIndex - 1] = stack[stack.lastIndex - 1] * stack.last()
                stack.removeAt(stack.lastIndex)
            }
            /*    / ,    
                */
            item == "/" -> {
                stack[stack.lastIndex - 1] = stack[stack.lastIndex - 1] / stack.last()
                stack.removeAt(stack.lastIndex)
            }
            /*    -,    
                 */
            item == "-" -> {
                stack[stack.lastIndex - 1] = stack[stack.lastIndex - 1] - stack.last()
                stack.removeAt(stack.lastIndex)
            }
        }
    }

    //  -  ,    
    println(": ${stack.first()}")
}