solution for day 7

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+namespace Solutions
+
+module Day7 =
+    open System.IO
+    open System.Text.RegularExpressions
+    
+    type Listing =
+    | LS
+    | CD of target: string
+    | Dir of name: string
+    | File of name: string * size: int
+
+    let (|RegexMatch|_|) pattern line =
+        let matched = Regex.Match(line, pattern)
+        if matched.Success then
+            let groups =
+                matched.Groups |> Seq.map (fun x -> x.Value) |> Seq.tail |> List.ofSeq
+            Some groups
+        else None
+
+    let parseListing = function
+    | RegexMatch "\$ cd (\/|\S+)" args -> CD args[0]
+    | RegexMatch "\$ ls" [] -> LS
+    | RegexMatch "dir (\S+)" name -> Dir name[0]
+    | RegexMatch "(\d+) (\S+)" data -> File (data[1], int data[0])
+    | _ -> failwith "shouldn't happen"
+
+    let input = File.ReadLines("inputs/day7.txt") |> Seq.map parseListing |> List.ofSeq
+
+
+    let dirSizes listings = 
+        let processListing (pwd, tree) listing =
+            match listing with 
+            | CD ".." -> (List.tail pwd, tree)
+            | CD target -> (target::pwd, tree)
+            | File (name, size) -> 
+                let rec addFileSize rem dirs =
+                    match rem with
+                    | [] -> dirs
+                    | _ :: t ->
+                        let addIfExists current = defaultArg current 0 + size
+                        let newDirs = Map.change rem (addIfExists >> Some) dirs
+                        addFileSize t newDirs
+                pwd, addFileSize pwd tree
+            | _ -> pwd, tree
+        listings |> List.fold processListing ([], Map.empty) |> snd
+    
+    let part1 () = dirSizes input |> Map.values |> Seq.filter (fun size -> size <= 100000) |> Seq.sum
+
+    let part2 () = 
+        let sizes = dirSizes input
+        let totalSpace = 70000000
+        let targetSpace = 30000000
+        let usedSpace = sizes[[ "/" ]]
+        let needToFree = usedSpace - (totalSpace - targetSpace)
+        sizes.Values |> Seq.sort |> Seq.find (fun x -> x >= needToFree)
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