Updating Maps

Part of the Logic & Flow section of Coddy's Kotlin journey. Lesson 3 of 63.

mutableMapOf allows adding and replacing entries with bracket assignment. remove(key) deletes an entry if present. A val can refer to a mutable map: the reference stays fixed while its contents change.

Inside main:

val counts = mutableMapOf("a" to 2)
counts["a"] = 5
counts["b"] = 3
println(counts.size)

Updating a changes its value; adding b introduces the second key.

Bracket assignment inserts a missing key or replaces an existing key's value.

Challenge

Medium

Complete updatedStock with parameters stock: Map<String, Int>, key: String, amount: Int. Copy stock into a mutable map, set the requested key to amount, and return the new number of keys.

Unless stricter bounds are stated above, collections contain at most 100 elements at each level, and integer arguments and integer collection values are between -1000 and 1000. Text supplied for parsing can include invalid or out-of-range representations as described.

Return a value of type Int. Keep the supplied input/output code. It reads scalar arguments one per line; a list starts with its count followed by its elements, and a map starts with its entry count followed by each key and value. Nested lists repeat the count-and-elements format for each row. The supplied main prints the return value followed by one newline. Lists use Kotlin's standard bracketed format; print no additional labels.

Try it yourself

fun updatedStock(stock: Map<String, Int>, key: String, amount: Int): Int {
    // Write your solution here.
    return 0
}
fun main() {
    val stockCount = readln().toInt()
    val stock = mutableMapOf<String, Int>()
    for (i0 in 0 until stockCount) {
        val stockKey = readln()
        val stockValue = readln().toInt()
        stock[stockKey] = stockValue
    }
    val key = readLine().orEmpty()
    val amount = readln().toInt()
    println(updatedStock(stock, key, amount))
}