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2024 Day 02 Complete!

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Advent of Code
br0xen (AoC++) 4*
--- Day 1: Historian Hysteria ---
The Chief Historian is always present for the big Christmas sleigh launch,
but nobody has seen him in months! Last anyone heard, he was visiting
locations that are historically significant to the North Pole; a group of
Senior Historians has asked you to accompany them as they check the places
they think he was most likely to visit.
As each location is checked, they will mark it on their list with a star.
They figure the Chief Historian must be in one of the first fifty places
they'll look, so in order to save Christmas, you need to help them get
fifty stars on their list before Santa takes off on December 25th.
Collect stars by solving puzzles. Two puzzles will be made available on
each day in the Advent calendar; the second puzzle is unlocked when you
complete the first. Each puzzle grants one star. Good luck!
You haven't even left yet and the group of Elvish Senior Historians has
already hit a problem: their list of locations to check is currently
empty. Eventually, someone decides that the best place to check first
would be the Chief Historian's office.
Upon pouring into the office, everyone confirms that the Chief Historian
is indeed nowhere to be found. Instead, the Elves discover an assortment
of notes and lists of historically significant locations! This seems to be
the planning the Chief Historian was doing before he left. Perhaps these
notes can be used to determine which locations to search?
Throughout the Chief's office, the historically significant locations are
listed not by name but by a unique number called the location ID. To make
sure they don't miss anything, The Historians split into two groups, each
searching the office and trying to create their own complete list of
location IDs.
There's just one problem: by holding the two lists up side by side (your
puzzle input), it quickly becomes clear that the lists aren't very
similar. Maybe you can help The Historians reconcile their lists?
For example:
3 4
4 3
2 5
1 3
3 9
3 3
Maybe the lists are only off by a small amount! To find out, pair up the
numbers and measure how far apart they are. Pair up the smallest number in
the left list with the smallest number in the right list, then the
second-smallest left number with the second-smallest right number, and so
on.
Within each pair, figure out how far apart the two numbers are; you'll
need to add up all of those distances. For example, if you pair up a 3
from the left list with a 7 from the right list, the distance apart is 4;
if you pair up a 9 with a 3, the distance apart is 6.
In the example list above, the pairs and distances would be as follows:
• The smallest number in the left list is 1, and the smallest number in
the right list is 3. The distance between them is 2.
• The second-smallest number in the left list is 2, and the
second-smallest number in the right list is another 3. The distance
between them is 1.
• The third-smallest number in both lists is 3, so the distance between
them is 0.
• The next numbers to pair up are 3 and 4, a distance of 1.
• The fifth-smallest numbers in each list are 3 and 5, a distance of 2.
• Finally, the largest number in the left list is 4, while the largest
number in the right list is 9; these are a distance 5 apart.
To find the total distance between the left list and the right list, add
up the distances between all of the pairs you found. In the example above,
this is 2 + 1 + 0 + 1 + 2 + 5, a total distance of 11!
Your actual left and right lists contain many location IDs. What is the
total distance between your lists?
Your puzzle answer was 2066446.
--- Part Two ---
Your analysis only confirmed what everyone feared: the two lists of
location IDs are indeed very different.
Or are they?
The Historians can't agree on which group made the mistakes or how to read
most of the Chief's handwriting, but in the commotion you notice an
interesting detail: a lot of location IDs appear in both lists! Maybe the
other numbers aren't location IDs at all but rather misinterpreted
handwriting.
This time, you'll need to figure out exactly how often each number from
the left list appears in the right list. Calculate a total similarity
score by adding up each number in the left list after multiplying it by
the number of times that number appears in the right list.
Here are the same example lists again:
3 4
4 3
2 5
1 3
3 9
3 3
For these example lists, here is the process of finding the similarity
score:
• The first number in the left list is 3. It appears in the right list
three times, so the similarity score increases by 3 * 3 = 9.
• The second number in the left list is 4. It appears in the right list
once, so the similarity score increases by 4 * 1 = 4.
• The third number in the left list is 2. It does not appear in the
right list, so the similarity score does not increase (2 * 0 = 0).
• The fourth number, 1, also does not appear in the right list.
• The fifth number, 3, appears in the right list three times; the
similarity score increases by 9.
• The last number, 3, appears in the right list three times; the
similarity score again increases by 9.
So, for these example lists, the similarity score at the end of this
process is 31 (9 + 4 + 0 + 0 + 9 + 9).
Once again consider your left and right lists. What is their similarity
score?
Your puzzle answer was 24931009.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should return to your Advent calendar and try
another puzzle.
If you still want to see it, you can get your puzzle input.
References

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package main
import (
"fmt"
"strconv"
"strings"
helpers "git.bullercodeworks.com/brian/adventofcode/helpers"
)
func main() {
inp := helpers.StdinToStringSlice()
part1(inp)
part2(inp)
}
func part1(inp []string) {
var ret int
for _, report := range inp {
wrk := cleanReport(report)
if testReport(wrk) {
ret++
}
}
fmt.Println("# Part 1")
fmt.Printf("%d reports are safe\n", ret)
}
func part2(inp []string) {
var ret int
for _, report := range inp {
wrk := cleanReport(report)
if testReport(wrk) {
ret++
} else {
if testDampenedReport(wrk) {
ret++
}
}
}
fmt.Println("# Part 2")
fmt.Printf("%d reports are safe\n", ret)
}
func cleanReport(inp string) []int {
var ret []int
wrk := strings.Split(inp, " ")
for i := range wrk {
w, err := strconv.Atoi(wrk[i])
if err != nil {
panic(err)
}
ret = append(ret, w)
}
return ret
}
func testReport(report []int) bool {
var prev int
var dir int
for idx, val := range report {
switch idx {
case 0:
prev = val
case 1:
if val < prev {
dir = -1
} else {
dir = 1
}
fallthrough
default:
if (val < prev && dir == 1) || (val > prev && dir == -1) {
return false
}
if dir == 1 {
if (val-prev < 1) || (val-prev > 3) {
return false
}
} else {
if (prev-val < 1) || (prev-val > 3) {
return false
}
}
prev = val
}
}
return true
}
func testDampenedReport(report []int) bool {
for i := range report {
wrk := removeIdx(report, i)
if testReport(wrk) {
return true
}
}
return false
}
func removeIdx(a []int, idx int) []int {
var ret []int
for i := range a {
if i == idx {
continue
}
ret = append(ret, a[i])
}
return ret
}

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Advent of Code
br0xen (AoC++) 4*
--- Day 2: Red-Nosed Reports ---
Fortunately, the first location The Historians want to search isn't a long
walk from the Chief Historian's office.
While the Red-Nosed Reindeer nuclear fusion/fission plant appears to
contain no sign of the Chief Historian, the engineers there run up to you
as soon as they see you. Apparently, they still talk about the time
Rudolph was saved through molecular synthesis from a single electron.
They're quick to add that - since you're already here - they'd really
appreciate your help analyzing some unusual data from the Red-Nosed
reactor. You turn to check if The Historians are waiting for you, but they
seem to have already divided into groups that are currently searching
every corner of the facility. You offer to help with the unusual data.
The unusual data (your puzzle input) consists of many reports, one report
per line. Each report is a list of numbers called levels that are
separated by spaces. For example:
7 6 4 2 1
1 2 7 8 9
9 7 6 2 1
1 3 2 4 5
8 6 4 4 1
1 3 6 7 9
This example data contains six reports each containing five levels.
The engineers are trying to figure out which reports are safe. The
Red-Nosed reactor safety systems can only tolerate levels that are either
gradually increasing or gradually decreasing. So, a report only counts as
safe if both of the following are true:
• The levels are either all increasing or all decreasing.
• Any two adjacent levels differ by at least one and at most three.
In the example above, the reports can be found safe or unsafe by checking
those rules:
• 7 6 4 2 1: Safe because the levels are all decreasing by 1 or 2.
• 1 2 7 8 9: Unsafe because 2 7 is an increase of 5.
• 9 7 6 2 1: Unsafe because 6 2 is a decrease of 4.
• 1 3 2 4 5: Unsafe because 1 3 is increasing but 3 2 is decreasing.
• 8 6 4 4 1: Unsafe because 4 4 is neither an increase or a decrease.
• 1 3 6 7 9: Safe because the levels are all increasing by 1, 2, or 3.
So, in this example, 2 reports are safe.
Analyze the unusual data from the engineers. How many reports are safe?
Your puzzle answer was 479.
--- Part Two ---
The engineers are surprised by the low number of safe reports until they
realize they forgot to tell you about the Problem Dampener.
The Problem Dampener is a reactor-mounted module that lets the reactor
safety systems tolerate a single bad level in what would otherwise be a
safe report. It's like the bad level never happened!
Now, the same rules apply as before, except if removing a single level
from an unsafe report would make it safe, the report instead counts as
safe.
More of the above example's reports are now safe:
• 7 6 4 2 1: Safe without removing any level.
• 1 2 7 8 9: Unsafe regardless of which level is removed.
• 9 7 6 2 1: Unsafe regardless of which level is removed.
• 1 3 2 4 5: Safe by removing the second level, 3.
• 8 6 4 4 1: Safe by removing the third level, 4.
• 1 3 6 7 9: Safe without removing any level.
Thanks to the Problem Dampener, 4 reports are actually safe!
Update your analysis by handling situations where the Problem Dampener can
remove a single level from unsafe reports. How many reports are now safe?
Your puzzle answer was 531.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should return to your Advent calendar and try
another puzzle.
If you still want to see it, you can get your puzzle input.
References

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7 6 4 2 1
1 2 7 8 9
9 7 6 2 1
1 3 2 4 5
8 6 4 4 1
1 3 6 7 9