1 files changed, 43 insertions, 0 deletions
diff --git a/day5.fsx b/day5.fsx
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+++ b/day5.fsx
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+open System.Security.Cryptography
+open System.Text
+
+let input = "reyedfim"
+
+let md5 (data: string): string = 
+    use md5 = MD5.Create()
+    (StringBuilder (), md5.ComputeHash(Encoding.ASCII.GetBytes data))
+    ||> Array.fold (fun sb b -> sb.Append(b.ToString("x2")))
+    |> string
+
+let rec getPassword (count: int) (chars: string): string =
+    if String.length chars = 8 then chars
+    else
+        let hashed = md5 (input + string count)
+        if hashed[0..4] = "00000" then 
+            getPassword (count + 1) (chars + string hashed[5])
+        else
+            getPassword (count + 1) chars
+
+// part 1
+getPassword 0 "" |> printfn "%s"
+
+// part 2
+let updateElement index newValue =
+    String.mapi (fun i v -> if i = index then newValue else v)
+
+let rec getPassword2 (count: int) (chars: string): string =
+    if Seq.fold (fun x y -> x && (y <> ' ')) true chars then chars
+    else
+        let hashed = md5 (input + string count)
+        if hashed[0..4] = "00000" then 
+            let index = int hashed[5] - int '0'
+            if index < 0 || index > 7 || chars[index] <> ' ' then
+                getPassword2 (count + 1) chars
+            else
+                let newChar = hashed[6]
+                let newChars = chars |> updateElement index newChar
+                getPassword2 (count + 1) newChars
+        else
+            getPassword2 (count + 1) chars
+
+getPassword2 0 "        " |> printfn "%s"
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