Careeroza

Real World Example

A Grocery Cart and Contacts

A quick-commerce app like Zepto or Blinkit keeps the menu as a read-only Map of prices, the cart as a MutableMap of item to quantity, and applied coupons as a MutableSet (a coupon cannot be applied twice). A chat app like WhatsApp keeps contacts in lists and finds common groups with set operations.

Example

Cart logic with all three collection types:

fun main() {
    val catalog = mapOf("Milk 1L" to 66, "Bread" to 45, "Eggs (6)" to 54, "Bananas (1kg)" to 60)
    val cart = mutableMapOf<String, Int>()
    val coupons = mutableSetOf<String>()

    fun addToCart(item: String, qty: Int = 1) {
        if (item !in catalog) {
            println("$item is not available")
            return
        }
        cart[item] = (cart[item] ?: 0) + qty
    }

    addToCart("Milk 1L", 2)
    addToCart("Bread")
    addToCart("Eggs (6)")
    addToCart("Bread")
    addToCart("Ice Cream")
    coupons.add("ZEPTO20")
    coupons.add("ZEPTO20")

    var subtotal = 0
    for ((item, qty) in cart) {
        val line = catalog.getValue(item) * qty
        subtotal += line
        println("${item.padEnd(10)} x$qty  ₹$line")
    }
    val discount = if ("ZEPTO20" in coupons) subtotal * 20 / 100 else 0
    println("Coupons: $coupons")
    println("Subtotal ₹$subtotal, discount ₹$discount, pay ₹${subtotal - discount}")

    val myGroups = setOf("Family", "College Friends", "Office")
    val friendGroups = setOf("College Friends", "Cricket Team")
    println("Groups in common: ${myGroups intersect friendGroups}")
}

Output

Ice Cream is not available
Milk 1L    x2  ₹132
Bread      x2  ₹90
Eggs (6)   x1  ₹54
Coupons: [ZEPTO20]
Subtotal ₹276, discount ₹55, pay ₹221
Groups in common: [College Friends]

Practice

Exercise: Create a mutableMapOf of student name to marks with three students. Add one more student, update one student's marks, then print each student as Name: marks and finally the class average.

Show answer
fun main() {
    val marks = mutableMapOf("Asha" to 82, "Ravi" to 74, "Neha" to 91)
    marks["Kiran"] = 68        // add
    marks["Ravi"] = 79         // update
    for ((name, m) in marks) println("$name: $m")
    println("Average: ${marks.values.average()}")   // 80.0
}