2024 Day 02 Complete!

2024/day01/problem

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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

2024/day02/main.go

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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
+}

2024/day02/problem

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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

2024/day02/testinput

@@ -0,0 +1,6 @@
+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