Summary - Maps and Sets

Combine Set and Map to write a phone book.

Summary: phone book with a set and a map

In this summary you will build a phone book. You use a MutableSet<String> to guarantee names are unique, and a MutableMap<String, String> to bind each name to a number.

val names = mutableSetOf("Ava", "Liam")
val phones = mutableMapOf("Ava" to "5551", "Liam" to "5552")
println(names)
println(phones)

The set drops duplicate names; the map binds a name to a number for quick lookup. Together they form a unique-key lookup table.

Exercise Build and print the phone book

Create a mutableSetOf("Ava", "Liam") and a mutableMapOf("Ava" to "5551", "Liam" to "5552"). Print the set first with println(names), then the map with println(phones).

Show example solution

fun main() {
    val names = mutableSetOf("Ava", "Liam")
    val phones = mutableMapOf("Ava" to "5551", "Liam" to "5552")
    println(names)
    println(phones)
}

Exercise Look up a number with get

Create a mutableMapOf("Ava" to "5551", "Liam" to "5552") and print Ava's number with println(phones.get("Ava")).

Show example solution

fun main() {
    val phones = mutableMapOf("Ava" to "5551", "Liam" to "5552")
    println(phones.get("Ava"))
}

Test yourself

Which pair suits a phone book?
- mutableSetOf<String> + mutableMapOf<String, String>
- listOf + listOf
- setOf + setOf
- mutableListOf + mutableMapOf (only list)
Show answer

mutableSetOf<String> + mutableMapOf<String, String> — Set keeps unique names, map holds number lookup.

Fill in the blank: add a pair to the book

phones.____("Nora", "5553")

Show answer

phones.put("Nora", "5553")

Next lesson: Defining functions

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