Решение

class MyQueue {
    private val inputStack = Stack<Int>()
    private val outputStack = Stack<Int>()

    fun push(x: Int) {
        inputStack.push(x)
    }

    fun pop(): Int {
        if (outputStack.isEmpty()) {
            while (!inputStack.isEmpty()) {
                outputStack.push(inputStack.pop())
            }
        }
        return outputStack.pop()
    }

    fun peek(): Int {
        if (outputStack.isEmpty()) {
            while (!inputStack.isEmpty()) {
                outputStack.push(inputStack.pop())
            }
        }
        return outputStack.peek()
    }

    fun empty(): Boolean {
        return inputStack.isEmpty() && outputStack.isEmpty()
    }
}