Add Largest And Smallest Elements (#140)

Author: igorwojda

README.md

@@ -83,8 +83,10 @@ multiple times and be persistent over time.
 - [Pyramid generator](src/test/kotlin/com/igorwojda/integer/pyramidgenerator)
 - [Steps generator](src/test/kotlin/com/igorwojda/integer/stepsgenerator)
 - [Fizz Buzz](src/test/kotlin/com/igorwojda/integer/fizzbuzz)
-- [Caesar Cipher](src/test/kotlin/com/igorwojda/string/caesarcipher)
+- [Caesar cipher](src/test/kotlin/com/igorwojda/string/caesarcipher)
 - [Has repeated char](src/test/kotlin/com/igorwojda/string/hasrepeatedcharacter)
+- [Smallest elements](src/test/kotlin/com/igorwojda/list/smallestelements)
+- [Largest elements](src/test/kotlin/com/igorwojda/list/largestelements)
 
 **Advanced** 
 
@@ -114,7 +116,7 @@ multiple times and be persistent over time.
 - [Radix sort](src/test/kotlin/com/igorwojda/list/sort/radixsort)
 - [Doubly linked list](src/test/kotlin/com/igorwojda/linkedlist/doubly/base)
 - [Max binary heap](src/test/kotlin/com/igorwojda/tree/heap/maxbinaryheap)
-- [Add Numbers](src/test/kotlin/com/igorwojda/linkedlist/singly/addnumbers)
+- [Add numbers](src/test/kotlin/com/igorwojda/linkedlist/singly/addnumbers)
 
 **Expert**
 
@@ -131,7 +133,7 @@ multiple times and be persistent over time.
 - [Min sub list length](src/test/kotlin/com/igorwojda/list/minsublistlength)
 - [Subtract](src/test/kotlin/com/igorwojda/list/subtract)
 - [Coins](src/test/kotlin/com/igorwojda/list/coins)
-- [Medan Of Sorted Lists](src/test/kotlin/com/igorwojda/list/medianoftwosorted)
+- [Medan of sorted lists](src/test/kotlin/com/igorwojda/list/medianoftwosorted)
 - [LRU Cache](src/test/kotlin/com/igorwojda/cache/lru)
 - [Advanced Cache](src/test/kotlin/com/igorwojda/cache/advancedlru)
 

misc/ChallengeGroups.md

@@ -42,7 +42,7 @@ loops which decreases complexity from `O(n^2)` to `O(n)`.
 - [Get duplicated arguments](../src/test/kotlin/com/igorwojda/string/getduplicatedarguments)
 - [Midpoint](../src/test/kotlin/com/igorwojda/linkedlist/singly/midpoint)
 - [Circular check](../src/test/kotlin/com/igorwojda/linkedlist/singly/circularcheck)
-- [Medan Of Sorted Lists](../src/test/kotlin/com/igorwojda/list/medianoftwosorted)
+- [Medan of sorted lists](../src/test/kotlin/com/igorwojda/list/medianoftwosorted)
 
 ## Frequency counter
 
@@ -71,7 +71,7 @@ We use sliding window instead of nested loops which decreases complexity from `O
 
 - [Linear search](../src/test/kotlin/com/igorwojda/list/search/linearsearch)
 - [Binary search](../src/test/kotlin/com/igorwojda/list/search/binarysearch)
-- [Medan Of Sorted Lists](../src/test/kotlin/com/igorwojda/list/medianoftwosorted)
+- [Medan of sorted lists](../src/test/kotlin/com/igorwojda/list/medianoftwosorted)
 
 ### Sort algorithms
 
@@ -95,14 +95,16 @@ We use sliding window instead of nested loops which decreases complexity from `O
 - [List subtract](../src/test/kotlin/com/igorwojda/list/subtract)
 - [Sum zero](../src/test/kotlin/com/igorwojda/list/sumzero)
 - [Coins](../src/test/kotlin/com/igorwojda/list/coins)
+- [Smallest elements](../src/test/kotlin/com/igorwojda/list/smallestelements)
+- [Largest elements](../src/test/kotlin/com/igorwojda/list/largestelements)
 
 ## Singly Linked List
 
 - [Singly linked list](../src/test/kotlin/com/igorwojda/linkedlist/singly/base)
 - [Circular linked list?](../src/test/kotlin/com/igorwojda/linkedlist/singly/circularcheck)
 - [Take n-th element from last](../src/test/kotlin/com/igorwojda/linkedlist/singly/fromlast)
 - [Midpoint](../src/test/kotlin/com/igorwojda/linkedlist/singly/midpoint)
-- [Add Numbers](../src/test/kotlin/com/igorwojda/linkedlist/singly/addnumbers)
+- [Add numbers](../src/test/kotlin/com/igorwojda/linkedlist/singly/addnumbers)
 
 ## Doubly Linked List
 
@@ -134,7 +136,7 @@ We use sliding window instead of nested loops which decreases complexity from `O
 
 ## String
 
-- [Caesar Cipher](../src/test/kotlin/com/igorwojda/string/caesarcipher)
+- [Caesar cipher](../src/test/kotlin/com/igorwojda/string/caesarcipher)
 - [Capitalize sentence](../src/test/kotlin/com/igorwojda/string/capitalizesentence)
 - [Decapitalize const](../src/test/kotlin/com/igorwojda/string/decapitalizeconst)
 - [Get duplicated arguments](../src/test/kotlin/com/igorwojda/string/getduplicatedarguments)
@@ -185,3 +187,8 @@ We use sliding window instead of nested loops which decreases complexity from `O
 
 - [LRU Cache](../src/test/kotlin/com/igorwojda/cache/lru)
 - [Advanced Cache](../src/test/kotlin/com/igorwojda/cache/advancedlru)
+
+## Priority Queue
+
+- [Smallest elements](../src/test/kotlin/com/igorwojda/list/smallestelements)
+- [Largest elements](../src/test/kotlin/com/igorwojda/list/largestelements)

src/test/kotlin/com/igorwojda/list/largestelements/Challenge.kt

@@ -0,0 +1,51 @@
+package com.igorwojda.list.largestelements
+
+import org.amshove.kluent.shouldBeEqualTo
+import org.junit.jupiter.api.Test
+import java.util.*
+
+private fun largestElements(list: List<Int>, count: Int): List<Int> {
+    if (list.size <= count) {
+        return list
+    }
+
+    val priorityQueue = PriorityQueue<Int>()
+
+    repeat(count) {
+        priorityQueue.add(list[it])
+    }
+
+    list
+        .drop(count)
+        .forEach {
+            if (it > priorityQueue.peek()) {
+                priorityQueue.poll()
+                priorityQueue.add(it)
+            }
+        }
+
+    return priorityQueue.toList()
+}
+
+private class Test {
+    @Test
+    fun `3 largest elements`() {
+        val list = listOf(5, 1, 3)
+
+        largestElements(list, 3) shouldBeEqualTo listOf(5, 1, 3)
+    }
+
+    @Test
+    fun `2 largest elements`() {
+        val list = listOf(5, 1, 3)
+
+        largestElements(list, 2) shouldBeEqualTo listOf(3, 5)
+    }
+
+    @Test
+    fun `1 largest element`() {
+        val list = listOf(5, 1, 3)
+
+        largestElements(list, 1) shouldBeEqualTo listOf(5)
+    }
+}

src/test/kotlin/com/igorwojda/list/largestelements/README.md

@@ -0,0 +1,31 @@
+# Largest Elements
+
+Implement a function that takes a list of integers and an integer `count` as input parameters. The purpose of the
+function is to find the largest `count` numbers from the provided list.
+
+If the size of the list is less than or equal to 'count', the function should return the original list.
+
+[Challenge](Challenge.kt) | [Solution](Solution.kt)
+
+## Examples
+
+Example 1
+
+```kotlin
+val list = listOf(5, 1, 3)
+largestElements(list, 2) shouldBeEqualTo listOf(3, 5)
+```
+
+Example 2
+
+```kotlin
+val list = listOf(5, 1, 3)
+largestElements(list, 3) shouldBeEqualTo listOf(5, 1, 3)
+```
+
+## Hints
+
+<details>
+<summary>Hint 1</summary>
+Use `PriorityQueue` to store the largest elements.
+</details>

src/test/kotlin/com/igorwojda/list/largestelements/Solution.kt

@@ -0,0 +1,31 @@
+package com.igorwojda.list.largestelements
+
+import java.util.*
+
+// Time complexity: O(n log k)
+private object Solution1 {
+    private fun largestElements(list: List<Int>, count: Int): List<Int> {
+        if (list.size <= count) {
+            return list
+        }
+
+        val priorityQueue = PriorityQueue<Int>()
+
+        repeat(count) {
+            priorityQueue.add(list[it])
+        }
+
+        list
+            .drop(count)
+            .forEach {
+                if (it > priorityQueue.peek()) {
+                    priorityQueue.poll()
+                    priorityQueue.add(it)
+                }
+            }
+
+        return priorityQueue.toList()
+    }
+}
+
+private object KtLintWillNotComplain

src/test/kotlin/com/igorwojda/list/smallestelements/Challenge.kt

@@ -0,0 +1,38 @@
+package com.igorwojda.list.smallestelements
+
+import org.amshove.kluent.shouldBeEqualTo
+import org.junit.jupiter.api.Test
+
+private fun smallestElements(list: List<Int>, count: Int): List<Int> {
+    TODO("Add your solution here")
+}
+
+private class Test {
+    @Test
+    fun `4 smallest elements`() {
+        val list = listOf(5, 1, 3)
+
+        smallestElements(list, 3) shouldBeEqualTo listOf(5, 1, 3)
+    }
+
+    @Test
+    fun `3 smallest elements`() {
+        val list = listOf(5, 1, 3)
+
+        smallestElements(list, 3) shouldBeEqualTo listOf(5, 1, 3)
+    }
+
+    @Test
+    fun `2 smallest elements`() {
+        val list = listOf(5, 1, 3)
+
+        smallestElements(list, 2) shouldBeEqualTo listOf(3, 1)
+    }
+
+    @Test
+    fun `1 smallest element`() {
+        val list = listOf(5, 1, 3)
+
+        smallestElements(list, 1) shouldBeEqualTo listOf(1)
+    }
+}

src/test/kotlin/com/igorwojda/list/smallestelements/README.md

@@ -0,0 +1,31 @@
+# Smallest Elements
+
+Implement a function that takes a list of integers and an integer `count` as input parameters. The purpose of the 
+function is to find the smallest `count` numbers from the provided list.
+
+If the size of the list is less than or equal to 'count', the function should return the original list. 
+
+[Challenge](Challenge.kt) | [Solution](Solution.kt)
+
+## Examples
+
+Example 1
+
+```kotlin
+val list = listOf(5, 1, 3)
+smallestElements(list, 2) shouldBeEqualTo listOf(3, 1)
+```
+
+Example 2
+
+```kotlin
+val list = listOf(5, 1, 3)
+smallestElements(list, 3) shouldBeEqualTo listOf(5, 1, 3)
+```
+
+## Hints
+
+<details>
+<summary>Hint 1</summary>
+Use `PriorityQueue` to store the smallest elements.
+</details>

src/test/kotlin/com/igorwojda/list/smallestelements/Solution.kt

@@ -0,0 +1,31 @@
+package com.igorwojda.list.smallestelements
+
+import java.util.*
+
+// Time complexity: O(n log k)
+private object Solution1 {
+    private fun smallestElements(list: List<Int>, count: Int): List<Int> {
+        if (list.size <= count) {
+            return list
+        }
+
+        val priorityQueue = PriorityQueue<Int>(Collections.reverseOrder())
+
+        repeat(count) {
+            priorityQueue.add(list[it])
+        }
+
+        list
+            .drop(count)
+            .forEach {
+                if (it < priorityQueue.peek()) {
+                    priorityQueue.poll()
+                    priorityQueue.add(it)
+                }
+            }
+
+        return priorityQueue.toList()
+    }
+}
+
+private object KtLintWillNotComplain