2024 Day 02 Complete!

2024/day02/main.go

@@ -0,0 +1,110 @@
+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

@@ -0,0 +1,94 @@
+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