From 021df22e8ab3ff7ee28597313b17b14c3ca7b097 Mon Sep 17 00:00:00 2001
From: Artem-Darius Weber <mit.3tlasa@gmail.com>
Date: Fri, 18 Apr 2025 07:11:57 +0300
Subject: [PATCH] lab 6 task 5

---
 lab6/Makefile           |  12 ++++-
 lab6/task5/Program.fs   | 107 ++++++++++++++++++++++++++++++++++++++++
 lab6/task5/task5.fsproj |   8 +++
 3 files changed, 126 insertions(+), 1 deletion(-)
 create mode 100644 lab6/task5/Program.fs
 create mode 100644 lab6/task5/task5.fsproj

diff --git a/lab6/Makefile b/lab6/Makefile
index c72547a..ae7de68 100644
--- a/lab6/Makefile
+++ b/lab6/Makefile
@@ -1,4 +1,4 @@
-.PHONY: run build clean task1 build-task1 clean-task1 task2 build-task2 clean-task2 task3 build-task3 clean-task3 task4 build-task4 clean-task4
+.PHONY: run build clean task1 build-task1 clean-task1 task2 build-task2 clean-task2 task3 build-task3 clean-task3 task4 build-task4 clean-task4 task5 build-task5 clean-task5
 
 # task1
 run:
@@ -51,3 +51,13 @@ build-task4:
 
 clean-task4:
 	cd task4 && dotnet clean
+
+# task5
+task5:
+	cd task5 && dotnet run --project task5.fsproj
+
+build-task5:
+	cd task5 && dotnet build
+
+clean-task5:
+	cd task5 && dotnet clean
diff --git a/lab6/task5/Program.fs b/lab6/task5/Program.fs
new file mode 100644
index 0000000..fc01c3b
--- /dev/null
+++ b/lab6/task5/Program.fs
@@ -0,0 +1,107 @@
+module Task5
+
+open System
+
+type ChurchList<'a> = ('a -> 'b -> 'b) -> 'b -> 'b
+
+let nil : ChurchList<'a> = fun _ z -> z
+
+let cons (x: 'a) (xs: ChurchList<'a>) : ChurchList<'a> = 
+    fun f z -> f x (xs f z)
+
+let toList (churchList: ChurchList<'a>) : 'a list =
+    churchList (fun x acc -> x :: acc) []
+    |> List.rev
+
+let ofList (lst: 'a list) : ChurchList<'a> =
+    List.foldBack cons lst nil
+
+let countFrequencies (churchList: ChurchList<'a>) : ('a * int) list when 'a : equality =
+    let regularList = toList churchList
+    
+    let rec countTailRec lst acc =
+        match lst with
+        | [] -> acc
+        | x :: xs ->
+            let rec updateCount freqList element =
+                match freqList with
+                | [] -> [(element, 1)]
+                | (key, count) :: rest ->
+                    if key = element then
+                        (key, count + 1) :: rest
+                    else
+                        (key, count) :: updateCount rest element
+            
+            let newAcc = updateCount acc x
+            countTailRec xs newAcc
+    
+    countTailRec regularList []
+
+let findMaxFrequency (frequencies: ('a * int) list) : ('a * int) option =
+    let rec findMaxTailRec lst currentMax =
+        match lst with
+        | [] -> currentMax
+        | (element, count) :: rest ->
+            match currentMax with
+            | None -> findMaxTailRec rest (Some (element, count))
+            | Some (_, maxCount) ->
+                if count > maxCount then
+                    findMaxTailRec rest (Some (element, count))
+                else
+                    findMaxTailRec rest currentMax
+    
+    findMaxTailRec frequencies None
+
+let findMostFrequent (churchList: ChurchList<'a>) : 'a option when 'a : equality =
+    let frequencies = countFrequencies churchList
+    match findMaxFrequency frequencies with
+    | Some (element, _) -> Some element
+    | None -> None
+
+let getMostFrequentCount (churchList: ChurchList<'a>) : int when 'a : equality =
+    let frequencies = countFrequencies churchList
+    match findMaxFrequency frequencies with
+    | Some (_, count) -> count
+    | None -> 0
+
+[<EntryPoint>]
+let main argv =
+    let testList1 = ofList [1; 2; 3; 2; 4; 2; 5; 3; 2]
+    let frequencies1 = countFrequencies testList1
+    frequencies1 |> List.iter (fun (elem, count) -> printfn "%A: %d" elem count)
+    
+    match findMostFrequent testList1 with
+    | Some element -> 
+        let count = getMostFrequentCount testList1
+        printfn "Most frequent: %A (%d times)" element count
+    | None -> printfn "Empty list"
+    
+    let testList2 = ofList ["apple"; "banana"; "apple"; "cherry"; "banana"; "apple"]
+    match findMostFrequent testList2 with
+    | Some element -> 
+        let count = getMostFrequentCount testList2
+        printfn "Most frequent string: %A (%d times)" element count
+    | None -> printfn "Empty list"
+    
+    let testList3 = ofList [5; 5; 5; 5]
+    match findMostFrequent testList3 with
+    | Some element -> 
+        let count = getMostFrequentCount testList3
+        printfn "All same: %A (%d times)" element count
+    | None -> printfn "Empty list"
+    
+    let testList4 = ofList [1; 2; 3; 4; 5]
+    match findMostFrequent testList4 with
+    | Some element -> 
+        let count = getMostFrequentCount testList4
+        printfn "All unique, first: %A (%d times)" element count
+    | None -> printfn "Empty list"
+    
+    let testList5 = nil
+    match findMostFrequent testList5 with
+    | Some element -> 
+        let count = getMostFrequentCount testList5
+        printfn "Should not happen: %A (%d times)" element count
+    | None -> printfn "Empty list handled correctly"
+    
+    0
\ No newline at end of file
diff --git a/lab6/task5/task5.fsproj b/lab6/task5/task5.fsproj
new file mode 100644
index 0000000..1cddbd7
--- /dev/null
+++ b/lab6/task5/task5.fsproj
@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>
\ No newline at end of file