Calculator algorythm - Error

[System32]

I found this code on the internet:

private fun evaluateExpression(expression: String): Int {
       val precedence = mapOf('+' to 1, '-' to 1, '*' to 2, '/' to 2)

       fun applyOperator(operator: Char, operand2: Int, operand1: Int): Int {
           return when (operator) {
               '+' -> operand1 + operand2
               '-' -> operand1 - operand2
               'x' -> operand1 * operand2
               '/' -> operand1 / operand2
               else -> throw IllegalArgumentException("Invalid operator: $operator")
           }
       }

       val stack = mutableListOf<Int>()
       var i = 0
       while (i < expression.length) {
           if (expression[i].isDigit()) {
               var j = i
               while (j < expression.length && expression[j].isDigit()) {
                   j++
               }
               val num = expression.substring(i, j).toInt()
               stack.add(num)
               i = j
           } else if (expression[i] in precedence.keys) {
               while (stack.isNotEmpty() && !stack.last().equals('(') && precedence[expression[i]]!! <= precedence[stack.last()]!!) {
                   val operand2 = stack.removeAt(stack.lastIndex)
                   val operand1 = stack.removeAt(stack.lastIndex)
                   val operator = stack.removeAt(stack.lastIndex)
                   val result = applyOperator(operator.toChar(), operand2, operand1)
                   stack.add(result)
               }
               stack.add(expression[i].toString().toInt())
               i++
           } else if (expression[i] == '(') {
               stack.add(expression[i].toString().toInt())
               i++
           } else if (expression[i] == ')') {
               while (stack.isNotEmpty() && !stack.last().equals('(')) {
                   val operand2 = stack.removeAt(stack.lastIndex)
                   val operand1 = stack.removeAt(stack.lastIndex)
                   val operator = stack.removeAt(stack.lastIndex)
                   val result = applyOperator(operator.toChar(), operand2, operand1)
                   stack.add(result)
               }
               stack.removeAt(stack.lastIndex) // Remove the opening parenthesis
               i++
           } else {
               i++
           }
       }

       while (stack.size > 1) {
           val operand2 = stack.removeAt(stack.lastIndex)
           val operand1 = stack.removeAt(stack.lastIndex)
           val operator = stack.removeAt(stack.lastIndex)
           val result = applyOperator(operator.toChar(), operand2, operand1)
           stack.add(result)
       }

       return stack.first()
   }

Now, the error I am getting here is: Type inference failed. The value of the type parameter K should be mentioned in input types (argument types, receiver type or expected type). Try to specify it explicitly.

It is related to this part of the code:


I have no idea how to solve this issue. I noticed that in Android studio with Kotlin, when you use last, it doesn't really work neatly.