Advent of Code 2015 - Day 10: Elves Look, Elves Say

Part 1

Description

Today, the Elves are playing a game called look-and-say. They take turns making sequences by reading aloud the previous sequence and using that reading as the next sequence. For example, 211 is read as "one two, two ones", which becomes 1221 (1 2, 2 1s).
Look-and-say sequences are generated iteratively, using the previous value as input for the next step. For each step, take the previous value, and replace each run of digits (like 111) with the number of digits (3) followed by the digit itself (1).
For example:

• 1 becomes 11 (1 copy of digit 1).
• 11 becomes 21 (2 copies of digit 1).
• 21 becomes 1211 (one 2 followed by one 1).
• 1211 becomes 111221 (one 1, one 2, and two 1s).
• 111221 becomes 312211 (three 1s, two 2s, and one 1).

Starting with the digits in your puzzle input, apply this process 40 times. What is the length of the result?

Input

Solution

This problem involves a sequence known as look and say sequence. And I found a ready to use VBA code here. I modified a bit into this:

Sub LookAndSay()
Dim s, news, curdigit, newdigit As String
Dim curlength, p, L As Long
 
ActiveSheet.Range("a4").Select
s = Selection.Value
For i = 1 To 40
  L = Len(s)
  p = 1
  curdigit = Left$(s, 1)
  curlength = 1
  news = ""
  For p = 2 To L
    newdigit = Mid$(s, p, 1)
    If curdigit = newdigit Then
      curlength = curlength + 1
    Else
      news = news & CStr(curlength) & curdigit
      curdigit = newdigit
      curlength = 1
    End If
  Next p
  news = news & CStr(curlength) & curdigit
  Debug.Print news
  s = news
  ActiveCell.Offset(1, 0).Select
  ActiveCell.Value = Len(s)
Next i
Exit Sub
End Sub

I modified the code so it will accommodate larger number (I change Integer into Long) and read input from and write output into the sheet. Then all I need is running the code and wait for the result.

Part 2

Description

Neat, right? You might also enjoy hearing John Conway talking about this sequence (that's Conway of Conway's Game of Life fame).
Now, starting again with the digits in your puzzle input, apply this process 50 times. What is the length of the new result?

Solution

For the part 2, I just need to modify the code to run 50 times.