Stream Processing
Robert Mion
Posted on August 3, 2022
Advent of Code 2017 Day 9
Try the simulator using your puzzle input!
Part 1
- Walking the line...again
- A
forloop and aflag - Writing and testing my algorithm
Walking the line...again
I'm reminded of 2021 Day 10: Syntax Scoring
A few differences:
- Syntax Scoring was a list of strings; this puzzle features one long string
- Syntax Scoring started with identifying
corruptedstrings: where an opening symbol was properly closed; this puzzle features a correct string...filled with garbage! - Syntax Scoring was a challenge of tracking and matching opening and closing symbols of the same type; this puzzle is similar, but with more to track given the inclusion of
garbagedata - Syntax Scoring algorithm walked the string; I anticipate doing the same in this puzzle
A for loop and a flag
I think those will be the core aspects of my algorithm:
Initialize a flag for garbage mode to false
For each character in the string
If in garbage mode
Check for exclamation marks
If one is encountered, skip a character
Keep walking
If not in garbage mode
If next character is <
Enter garbage mode
Else, if next character is {
Account for another group, possibly at the same or next level
Else if next character is }
Update the accumulating score to account for the group that just closed
Else if next character is anything else
Keep walking
There's probably some finer details in the conditions that I'm missing, but that's an outline of the algorithm I intend to write.
Let's see how far off I was...assuming I can write a working algorithm!
Writing and testing my algorithm
Thankfully, the instructions offer plenty of unit tests.
I'm going to write this algorithm piece by piece, condition by condition, ensuring I pass some simpler tests, then the more complicated ones...then hopefully my puzzle input.
Getting examples 1-4 to work
{} = 1
{{{}}} = 6
{{},{}} = 5
{{{},{},{{}}}} = 16
My working algorithm:
Setup:
Split the input at each character into an array of characters
Create score, starting at 0
Create level, starting at 1
Loop:
For each character in the stream except the last
Depending on what the next character is:
If it is a {
Increment level by 1
Else, if it is a }
Increment score by level
Decrement level
Return score
Now, to start accounting for garbage.
Getting example 6, 7 and 9 to work
{<a>,<a>,<a>,<a>} = 1
{{<a>},{<a>},{<a>},{<a>}} = 9
{{<ab>},{<ab>},{<ab>},{<ab>}} = 9
My working algorithm:
Setup:
Split the input at each character into an array of characters
Create score, starting at 0
Create level, starting at 1
Create flag for garbage mode, starting at false
Loop:
For each character in the stream except the last
Depending on what the next character is:
If garbage mode is on
If it is a >
Turn garbage mode off
Else, garbage mode is off
If it is a {
Increment level by 1
Else, if it is a }
Increment score by level
Decrement level
Else, if it is a <
Turn garbage mode on
Return score
Getting examples 8, 10 and 11 to work
{{<!>},{<!>},{<!>},{<a>}} = 3
{{<!!>},{<!!>},{<!!>},{<!!>}} = 9
{{<a!>},{<a!>},{<a!>},{<ab>}} = 3
My working algorithm:
Setup:
Split the input at each character into an array of characters
Create score, starting at 0
Create level, starting at 1
Create flag for garbage mode, starting at false
Loop:
For each character in the stream except the last
Depending on what the next character is:
If garbage mode is on
If it is a >
Turn garbage mode off
If it is a !
Increment the character location tracker by 1 to skip a character in the stream
Else, garbage mode is off
If it is a {
Increment level by 1
Else, if it is a }
Increment score by level
Decrement level
Else, if it is a <
Turn garbage mode on
Return score
Testing on my puzzle input
- It finished!
- It generated the correct answer!
Part 2
- Garbage collection, of course!
Garbage collection, of course!
I'm hopeful I just need to add a tracking counter, and a statement that increments it by one in the proper case in one of my switch statements.
My working algorithm:
Setup:
Split the input at each character into an array of characters
Create score, starting at 0
Create level, starting at 1
Create flag for garbage mode, starting at false
Create garbage, starting at 0
Loop:
For each character in the stream except the last
Depending on what the next character is:
If garbage mode is on
If it is a >
Turn garbage mode off
If it is a !
Increment the character location tracker by 1 to skip a character in the stream
Otherwise
Increment garbage by 1
Else, garbage mode is off
If it is a {
Increment level by 1
Else, if it is a }
Increment score by level
Decrement level
Else, if it is a <
Turn garbage mode on
Return garbage
That's all it took to generate the correct answer for Part 2!
I did it!!
- I solved both parts!
- I did so by writing my algorithm piece by piece, solving only a few examples at a time
- I used a few
switchstatements, which I don't use too often throughout these puzzles; I often opt for dictionaries so I can leverage key-value look-ups - I built a simulator to watch the stream get processed in front of my eyes!
I'm glad I didn't try solving this puzzle all at once, or I may have struggled more than necessary.
Posted on August 3, 2022
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