Resolutions

src/i_introduction/_0_Hello_World/n00Start.kt

@@ -24,6 +24,4 @@ fun todoTask0(): Nothing = TODO(
     references = { task0(); "OK" }
 )
 
-fun task0(): String {
-    return todoTask0()
-}
+fun task0() = "OK"

src/i_introduction/_10_Object_Expressions/n10ObjectExpressions.kt

@@ -18,6 +18,8 @@ fun todoTask10(): Nothing = TODO(
 
 fun task10(): List<Int> {
     val arrayList = arrayListOf(1, 5, 2)
-    Collections.sort(arrayList, todoTask10())
+    Collections.sort(arrayList, object : Comparator<Int> {
+        override fun compare(x: Int, y: Int) = y - x
+    })
     return arrayList
 }

src/i_introduction/_11_SAM_Conversions/n11SAMConversions.kt

@@ -15,6 +15,6 @@ fun todoTask11(): Nothing = TODO(
 
 fun task11(): List<Int> {
     val arrayList = arrayListOf(1, 5, 2)
-    Collections.sort(arrayList, { x, y -> todoTask11() })
+    Collections.sort(arrayList, { x, y -> y - x })
     return arrayList
 }

src/i_introduction/_12_Extensions_On_Collections/n12ExtensionsOnCollections.kt

@@ -17,7 +17,6 @@ fun todoTask12(): Nothing = TODO(
 )
 
 fun task12(): List<Int> {
-    todoTask12()
-    return arrayListOf(1, 5, 2)
+    return arrayListOf(1, 5, 2).sortedDescending()
 }
 

src/i_introduction/_1_Java_To_Kotlin_Converter/n01JavaToKotlinConverter.kt

@@ -14,5 +14,16 @@ fun todoTask1(collection: Collection<Int>): Nothing = TODO(
 
 
 fun task1(collection: Collection<Int>): String {
-    todoTask1(collection)
+    val sb = StringBuilder()
+    sb.append("{")
+    val iterator = collection.iterator()
+    while (iterator.hasNext()) {
+        val element = iterator.next()
+        sb.append(element)
+        if (iterator.hasNext()) {
+            sb.append(", ")
+        }
+    }
+    sb.append("}")
+    return sb.toString()
 }

src/i_introduction/_2_Named_Arguments/n02NamedArguments.kt

@@ -24,6 +24,5 @@ fun todoTask2(): Nothing = TODO(
     references = { collection: Collection<Int> -> task1(collection); collection.joinToString() })
 
 fun task2(collection: Collection<Int>): String {
-    todoTask2()
-    return collection.joinToString()
+    return collection.joinToString(prefix = "{", postfix = "}")
 }

src/i_introduction/_3_Default_Arguments/n03DefaultArguments.kt

@@ -14,12 +14,12 @@ fun todoTask3(): Nothing = TODO(
     documentation = doc2(),
     references = { name: String -> JavaCode3().foo(name); foo(name) })
 
-fun foo(name: String): String = todoTask3()
+fun foo(name: String, number: Int = 42, toUpperCase: Boolean = false) =
+        (if (toUpperCase) name.toUpperCase() else name) + number
 
 fun task3(): String {
-    todoTask3()
-//    return (foo("a") +
-//            foo("b", number = 1) +
-//            foo("c", toUpperCase = true) +
-//            foo(name = "d", number = 2, toUpperCase = true))
+    return (foo("a") +
+            foo("b", number = 1) +
+            foo("c", toUpperCase = true) +
+            foo(name = "d", number = 2, toUpperCase = true))
 }

src/i_introduction/_4_Lambdas/n04Lambdas.kt

@@ -22,4 +22,4 @@ fun todoTask4(collection: Collection<Int>): Nothing = TODO(
     documentation = doc4(),
     references = { JavaCode4().task4(collection) })
 
-fun task4(collection: Collection<Int>): Boolean = todoTask4(collection)
+fun task4(collection: Collection<Int>): Boolean = collection.any { it % 2 == 0 }

src/i_introduction/_5_String_Templates/n05StringTemplates.kt

@@ -35,4 +35,4 @@ fun todoTask5(): Nothing = TODO(
     documentation = doc5(),
     references = { getPattern(); month })
 
-fun task5(): String = todoTask5()
+fun task5(): String = """\d{2} $month \d{4}"""

src/i_introduction/_6_Data_Classes/n06DataClasses.kt

@@ -15,10 +15,10 @@ fun todoTask6(): Nothing = TODO(
     references = { JavaCode6.Person("Alice", 29) }
 )
 
-class Person
+data class Person(val name: String, val age: Int)
 
 fun task6(): List<Person> {
-    todoTask6()
-    return listOf(/*Person("Alice", 29), Person("Bob", 31)*/)
+//    todoTask6()
+    return listOf(Person("Alice", 29), Person("Bob", 31))
 }
 

src/i_introduction/_7_Nullable_Types/n07NullableTypes.kt

@@ -25,7 +25,13 @@ fun todoTask7(client: Client?, message: String?, mailer: Mailer): Nothing = TODO
 fun sendMessageToClient(
     client: Client?, message: String?, mailer: Mailer
 ) {
-    todoTask7(client, message, mailer)
+//    todoTask7(client, message, mailer)
+    val email = client?.personalInfo?.email
+
+    if (email != null && message != null) {
+
+        mailer.sendMessage(email, message)
+    }
 }
 
 class Client(val personalInfo: PersonalInfo?)

src/i_introduction/_8_Smart_Casts/n08SmartCasts.kt

@@ -12,8 +12,8 @@ class Sum(val left: Expr, val right: Expr) : Expr()
 
 fun eval(e: Expr): Int =
     when (e) {
-        is Num -> todoTask8(e)
-        is Sum -> todoTask8(e)
+        is Num -> e.value
+        is Sum -> eval(e.left) + eval(e.right)
     }
 
 fun todoTask8(expr: Expr): Nothing = TODO(

src/i_introduction/_9_Extension_Functions/n09ExtensionFunctions.kt

@@ -29,7 +29,7 @@ fun todoTask9(): Nothing = TODO(
 
 data class RationalNumber(val numerator: Int, val denominator: Int)
 
-fun Int.r(): RationalNumber = todoTask9()
-fun Pair<Int, Int>.r(): RationalNumber = todoTask9()
+fun Int.r(): RationalNumber = RationalNumber(this, 1)
+fun Pair<Int, Int>.r(): RationalNumber = RationalNumber(this.first, this.second)
 
 

src/ii_collections/n13Introduction.kt

@@ -18,7 +18,6 @@ fun example0(list: List<Int>) {
 
 fun Shop.getSetOfCustomers(): Set<Customer> {
     // Return a set containing all the customers of this shop
-    todoCollectionTask()
-//    return this.customers
+    return customers.toSet()
 }
 

src/ii_collections/n14FilterMap.kt

@@ -10,12 +10,12 @@ fun example1(list: List<Int>) {
 
 fun Shop.getCitiesCustomersAreFrom(): Set<City> {
     // Return the set of cities the customers are from
-    todoCollectionTask()
+    return customers.map { it.city }.toSet()
 }
 
 fun Shop.getCustomersFrom(city: City): List<Customer> {
     // Return a list of the customers who live in the given city
-    todoCollectionTask()
+    return customers.filter { it.city == city }
 }
 
 

src/ii_collections/n15AllAnyAndOtherPredicates.kt

@@ -15,25 +15,26 @@ fun example2(list: List<Int>) {
 
 fun Customer.isFrom(city: City): Boolean {
     // Return true if the customer is from the given city
-    todoCollectionTask()
+    return this.city == city
 }
 
 fun Shop.checkAllCustomersAreFrom(city: City): Boolean {
     // Return true if all customers are from the given city
-    todoCollectionTask()
+    return customers.all { it.isFrom(city) }
 }
 
 fun Shop.hasCustomerFrom(city: City): Boolean {
     // Return true if there is at least one customer from the given city
-    todoCollectionTask()
+    return customers.any { it.isFrom(city) }
 }
 
 fun Shop.countCustomersFrom(city: City): Int {
     // Return the number of customers from the given city
-    todoCollectionTask()
+    return customers.count { it.isFrom(city) }
 }
 
 fun Shop.findFirstCustomerFrom(city: City): Customer? {
     // Return the first customer who lives in the given city, or null if there is none
-    todoCollectionTask()
+    return customers.firstOrNull { it.isFrom(city) }
 }
+

src/ii_collections/n16FlatMap.kt

@@ -10,11 +10,11 @@ fun example() {
 val Customer.orderedProducts: Set<Product>
     get() {
         // Return all products this customer has ordered
-        todoCollectionTask()
+        return orders.flatMap { it.products }.toSet()
     }
 
 val Shop.allOrderedProducts: Set<Product>
     get() {
         // Return all products that were ordered by at least one customer
-        todoCollectionTask()
+        return customers.flatMap { it.orderedProducts }.toSet()
     }

src/ii_collections/n17MaxMin.kt

@@ -7,10 +7,10 @@ fun example4() {
 
 fun Shop.getCustomerWithMaximumNumberOfOrders(): Customer? {
     // Return a customer whose order count is the highest among all customers
-    todoCollectionTask()
+    return customers.maxBy { it.orders.size }
 }
 
 fun Customer.getMostExpensiveOrderedProduct(): Product? {
     // Return the most expensive product which has been ordered
-    todoCollectionTask()
+    return orderedProducts.maxBy { it.price }
 }

src/ii_collections/n18Sort.kt

@@ -8,5 +8,5 @@ fun example5() {
 
 fun Shop.getCustomersSortedByNumberOfOrders(): List<Customer> {
     // Return a list of customers, sorted by the ascending number of orders they made
-    todoCollectionTask()
+    return customers.sortedBy { it.orders.size }
 }

src/ii_collections/n19Sum.kt

@@ -8,5 +8,5 @@ fun example6() {
 fun Customer.getTotalOrderPrice(): Double {
     // Return the sum of prices of all products that a customer has ordered.
     // Note: a customer may order the same product several times.
-    todoCollectionTask()
+    return orders.flatMap { it.products }.sumByDouble { it.price }
 }

src/ii_collections/n20GroupBy.kt

@@ -8,5 +8,5 @@ fun example7() {
 
 fun Shop.groupCustomersByCity(): Map<City, List<Customer>> {
     // Return a map of the customers living in each city
-    todoCollectionTask()
+    return customers.groupBy { it.city }
 }

src/ii_collections/n21Partition.kt

@@ -12,5 +12,9 @@ fun example8() {
 
 fun Shop.getCustomersWithMoreUndeliveredOrdersThanDelivered(): Set<Customer> {
     // Return customers who have more undelivered orders than delivered
-    todoCollectionTask()
+    return customers.filter {
+        val (delivered, undelivered) = it.orders.partition { it.isDelivered }
+        undelivered.size > delivered.size
+    }.toSet()
 }
+

src/ii_collections/n22Fold.kt

@@ -15,6 +15,6 @@ fun whatFoldDoes(): Int {
 fun Shop.getSetOfProductsOrderedByEachCustomer(): Set<Product> {
     // Return the set of products that were ordered by each of the customers
     return customers.fold(allOrderedProducts, { orderedByAll, customer ->
-        todoCollectionTask()
+        orderedByAll.intersect(customer.orderedProducts)
     })
 }

src/ii_collections/n23CompoundTasks.kt

@@ -2,17 +2,17 @@ package ii_collections
 
 fun Shop.getCustomersWhoOrderedProduct(product: Product): Set<Customer> {
     // Return the set of customers who ordered the specified product
-    todoCollectionTask()
+    return customers.filter { it.orderedProducts.contains(product) }.toSet()
 }
 
 fun Customer.getMostExpensiveDeliveredProduct(): Product? {
     // Return the most expensive product among all delivered products
     // (use the Order.isDelivered flag)
-    todoCollectionTask()
+    return orders.filter { it.isDelivered }.flatMap { it.products }.maxBy { it.price }
 }
 
 fun Shop.getNumberOfTimesProductWasOrdered(product: Product): Int {
     // Return the number of times the given product was ordered.
     // Note: a customer may order the same product for several times.
-    todoCollectionTask()
+    return customers.flatMap { it.orders }.flatMap { it.products }.count { it == product }
 }

src/ii_collections/n24ExtensionsOnCollections.kt

@@ -12,8 +12,8 @@ fun todoTask24(): Nothing = TODO(
 )
 
 fun doSomethingStrangeWithCollection(collection: Collection<String>): Collection<String>? {
-    val groupsByLength = collection.groupBy { s -> todoTask24() }
+    val groupsByLength = collection.groupBy { s -> s.length }
 
-    return groupsByLength.values.maxBy { group -> todoTask24() }
+    return groupsByLength.values.maxBy { group -> group.size }
 }
 

src/iii_conventions/MyDate.kt

@@ -1,13 +1,41 @@
 package iii_conventions
 
-data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int)
+data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int): Comparable<MyDate> {
+    override fun compareTo(other: MyDate) = when {
+        year != other.year -> year - other.year
+        month != other.month -> month - other.month
+        else -> dayOfMonth - other.dayOfMonth
+    }
+}
+
+operator fun MyDate.rangeTo(other: MyDate) = DateRange(this, other)
+
+class DateRange(
+        override val start: MyDate,
+        override val endInclusive: MyDate
+) : ClosedRange<MyDate>, Iterable<MyDate> {
+    override fun iterator(): Iterator<MyDate> = DateIterator(this)
+    override fun contains(value: MyDate): Boolean = start <= value && value <= endInclusive
+}
 
-operator fun MyDate.rangeTo(other: MyDate): DateRange = todoTask27()
+class DateIterator(val dateRange: DateRange) : Iterator<MyDate> {
+    var current: MyDate = dateRange.start
+    override fun next(): MyDate {
+        val result = current
+        current = current.nextDay()
+        return result
+    }
+    override fun hasNext(): Boolean = current <= dateRange.endInclusive
+}
 
 enum class TimeInterval {
     DAY,
     WEEK,
     YEAR
 }
 
-class DateRange(val start: MyDate, val endInclusive: MyDate)
+class RepeatedTimeInterval(val timeInterval: TimeInterval, val number: Int)
+operator fun TimeInterval.times(number: Int) = RepeatedTimeInterval(this, number)
+
+operator fun MyDate.plus(timeInterval: TimeInterval) = addTimeIntervals(timeInterval, 1)
+operator fun MyDate.plus(timeIntervals: RepeatedTimeInterval) = addTimeIntervals(timeIntervals.timeInterval, timeIntervals.number)

src/iii_conventions/n25Comparison.kt

@@ -16,7 +16,7 @@ fun todoTask25(): Nothing = TODO(
 )
 
 fun task25(date1: MyDate, date2: MyDate): Boolean {
-    todoTask25()
-//    return date1 < date2
+//    todoTask25()
+    return date1 < date2
 }
 

src/iii_conventions/n26InRange.kt

@@ -18,6 +18,6 @@ fun todoTask26_(): Nothing = TODO(
 )
 
 fun checkInRange(date: MyDate, first: MyDate, last: MyDate): Boolean {
-    todoTask26_()
-//    return date in DateRange(first, last)
+//    todoTask26_()
+    return date in DateRange(first, last)
 }

src/iii_conventions/n27RangeTo.kt

@@ -15,6 +15,6 @@ fun todoTask27(): Nothing = TODO(
 )
 
 fun checkInRange2(date: MyDate, first: MyDate, last: MyDate): Boolean {
-    todoTask27()
-//    return date in first..last
+//    todoTask27()
+    return date in first..last
 }

src/iii_conventions/n28ForLoop.kt

@@ -37,8 +37,8 @@ fun todoTask28(): Nothing = TODO(
 
 
 fun iterateOverDateRange(firstDate: MyDate, secondDate: MyDate, handler: (MyDate) -> Unit) {
-    todoTask28()
-//    for (date in firstDate..secondDate) {
-//        handler(date)
-//    }
+//    todoTask28()
+    for (date in firstDate..secondDate) {
+        handler(date)
+    }
 }