DynamicArray.kt

package day4

import kotlinx.atomicfu.*

// This implementation never stores `null` values.
class DynamicArray<E: Any> {
    private val core = atomic(Core(capacity = 1)) // Do not change the initial capacity

    /**
     * Adds the specified [element] to the end of this array.
     */
    fun addLast(element: E) {
        // TODO: Implement me!
        // TODO: Yeah, this is a hard task, I know ...
    }

    /**
     * Puts the specified [element] into the cell [index],
     * or throws [IllegalArgumentException] if [index]
     * exceeds the size of this array.
     */
    fun set(index: Int, element: E) {
        val curCore = core.value
        val curSize = curCore.size.value
        require(index < curSize) { "index must be lower than the array size" }
        // TODO: check that the cell is not "frozen"
        curCore.array[index].value = element
    }

    /**
     * Returns the element located in the cell [index],
     * or throws [IllegalArgumentException] if [index]
     * exceeds the size of this array.
     */
    @Suppress("UNCHECKED_CAST")
    fun get(index: Int): E {
        val curCore = core.value
        val curSize = curCore.size.value
        require(index < curSize) { "index must be lower than the array size" }
        // TODO: check that the cell is not "frozen",
        // TODO: unwrap the element in this case.
        return curCore.array[index].value as E
    }

    private class Core(
        val capacity: Int
    ) {
        val array = atomicArrayOfNulls<Any?>(capacity)
        val size = atomic(0)
        val next = atomic<Core?>(null)
    }
}