ImmutableIntList.kt

fun main() {
    val list1 = ImmutableIntList(0)
    println(list1)

    val list2 = list1.add(1).add(2).add(4).add(5)
    println(list2)

    val list3 = list2.addAt(3,2)
    println(list3)

    val list4 = list3.deleteAt(list3.size - 1).deleteAt(0)
    println(list4)
}


class ImmutableIntList(val size: Int) {
    private val items = IntArray(size)

    init {
        if (size < 0) {
            throw IllegalArgumentException("Size must be great or equals 0")
        }
    }

    fun add(item: Int): ImmutableIntList {
        return addAt(item, size)
    }

    fun addAt(item: Int, idx: Int): ImmutableIntList {
        if (idx > size) {
            throw IndexOutOfBoundsException("Index greater that size: $idx > $size")
        }

        val newList = ImmutableIntList(size + 1)

        if (size == 0) {
            newList.items[0] = item
            return newList
        }

        for (i in 0 until idx) {
            newList.items[i] = items[i]
        }

        newList.items[idx] = item

        for (i in idx until items.size) {
            newList.items[i + 1] = items[i]
        }

        return newList
    }

    fun deleteAt(idx: Int): ImmutableIntList {
        if (size == 0) throw IllegalArgumentException("List is already clear")
        assertIdxLessSize(idx)

        val newList = ImmutableIntList(size - 1)

        for (i in 0 until idx) {
            newList.items[i] = items[i]
        }

        for (i in (idx + 1) until items.size) {
            newList.items[i - 1] = items[i]
        }

        return newList
    }

    operator fun get(idx: Int): Int {
        assertIdxLessSize(idx)
        return items[idx]
    }

    private fun assertIdxLessSize(idx: Int) {
        if (idx >= size) {
            throw IndexOutOfBoundsException("Index greater or equals size: $idx >= $size")
        }
    }

    override fun toString(): String {
        return "[" + items.joinToString() + "]"
    }
}