11/code.go

@@ -0,0 +1,109 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+func readInput(file *os.File) map[string][]string {
+	scanner := bufio.NewScanner(file)
+	devices := make(map[string][]string)
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			continue
+		}
+
+		parts := strings.Split(line, ": ")
+		if len(parts) < 2 {
+			log.Fatalf("Bad input: %s", line)
+		}
+
+		name := parts[0]
+		connections := strings.Split(parts[1], " ")
+		devices[name] = connections
+	}
+
+	return devices
+}
+
+func part1(entry string, devices map[string][]string) int {
+	if entry == "out" {
+		return 1
+	}
+
+	var count int
+	for _, device := range devices[entry] {
+		count += part1(device, devices)
+	}
+
+	return count
+}
+
+func passedDACandFFT(path []string) bool {
+	var dac, fft bool
+	for i := range path {
+		if path[i] == "dac" {
+			dac = true
+		}
+
+		if path[i] == "fft" {
+			fft = true
+		}
+	}
+
+	return dac && fft
+}
+
+func part2(entry string, devices map[string][]string) int {
+	var count int
+	visited := make(map[string]bool)
+	path := []string{}
+
+	var dfs func(current string)
+	dfs = func(current string) {
+		path = append(path, current)
+		visited[current] = true
+		defer func() {
+			path = path[:len(path)-1]
+			visited[current] = false
+		}()
+
+		if current == "out" {
+			if passedDACandFFT(path) {
+				count++
+			}
+
+			return
+		} else {
+			for _, neighbor := range devices[current] {
+				if !visited[neighbor] {
+					dfs(neighbor)
+				}
+			}
+		}
+	}
+
+	dfs(entry)
+	return count
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatal("You need to specify a file!")
+	}
+
+	filePath := os.Args[1]
+	file, err := os.Open(filePath)
+	if err != nil {
+		log.Fatalf("Failed to open %s!\n", filePath)
+	}
+
+	devices := readInput(file)
+	fmt.Println("Part1:", part1("you", devices))
+	fmt.Println("Part2:", part2("svr", devices))
+}

11/description.txt

@@ -0,0 +1,77 @@
+--- Day 11: Reactor ---
+
+You hear some loud beeping coming from a hatch in the floor of the factory, so you decide to check it out. Inside, you find several large electrical conduits and a ladder.
+
+Climbing down the ladder, you discover the source of the beeping: a large, toroidal reactor which powers the factory above. Some Elves here are hurriedly running between the reactor and a nearby server rack, apparently trying to fix something.
+
+One of the Elves notices you and rushes over. "It's a good thing you're here! We just installed a new server rack, but we aren't having any luck getting the reactor to communicate with it!" You glance around the room and see a tangle of cables and devices running from the server rack to the reactor. She rushes off, returning a moment later with a list of the devices and their outputs (your puzzle input).
+
+For example:
+
+aaa: you hhh
+you: bbb ccc
+bbb: ddd eee
+ccc: ddd eee fff
+ddd: ggg
+eee: out
+fff: out
+ggg: out
+hhh: ccc fff iii
+iii: out
+Each line gives the name of a device followed by a list of the devices to which its outputs are attached. So, bbb: ddd eee means that device bbb has two outputs, one leading to device ddd and the other leading to device eee.
+
+The Elves are pretty sure that the issue isn't due to any specific device, but rather that the issue is triggered by data following some specific path through the devices. Data only ever flows from a device through its outputs; it can't flow backwards.
+
+After dividing up the work, the Elves would like you to focus on the devices starting with the one next to you (an Elf hastily attaches a label which just says you) and ending with the main output to the reactor (which is the device with the label out).
+
+To help the Elves figure out which path is causing the issue, they need you to find every path from you to out.
+
+In this example, these are all of the paths from you to out:
+
+Data could take the connection from you to bbb, then from bbb to ddd, then from ddd to ggg, then from ggg to out.
+Data could take the connection to bbb, then to eee, then to out.
+Data could go to ccc, then ddd, then ggg, then out.
+Data could go to ccc, then eee, then out.
+Data could go to ccc, then fff, then out.
+In total, there are 5 different paths leading from you to out.
+
+How many different paths lead from you to out?
+
+Your puzzle answer was 472.
+
+The first half of this puzzle is complete! It provides one gold star: *
+
+--- Part Two ---
+
+Thanks in part to your analysis, the Elves have figured out a little bit about the issue. They now know that the problematic data path passes through both dac (a digital-to-analog converter) and fft (a device which performs a fast Fourier transform).
+
+They're still not sure which specific path is the problem, and so they now need you to find every path from svr (the server rack) to out. However, the paths you find must all also visit both dac and fft (in any order).
+
+For example:
+
+svr: aaa bbb
+aaa: fft
+fft: ccc
+bbb: tty
+tty: ccc
+ccc: ddd eee
+ddd: hub
+hub: fff
+eee: dac
+dac: fff
+fff: ggg hhh
+ggg: out
+hhh: out
+This new list of devices contains many paths from svr to out:
+
+svr,aaa,fft,ccc,ddd,hub,fff,ggg,out
+svr,aaa,fft,ccc,ddd,hub,fff,hhh,out
+svr,aaa,fft,ccc,eee,dac,fff,ggg,out
+svr,aaa,fft,ccc,eee,dac,fff,hhh,out
+svr,bbb,tty,ccc,ddd,hub,fff,ggg,out
+svr,bbb,tty,ccc,ddd,hub,fff,hhh,out
+svr,bbb,tty,ccc,eee,dac,fff,ggg,out
+svr,bbb,tty,ccc,eee,dac,fff,hhh,out
+However, only 2 paths from svr to out visit both dac and fft.
+
+Find all of the paths that lead from svr to out. How many of those paths visit both dac and fft?

11/input

@@ -0,0 +1,599 @@
+vwm: xoe ydz tbn
+erq: qws zsm fmb rya
+wzf: mxt arh gjd
+qee: you wjk
+zhy: tyc
+pgy: out
+rkn: ads ybl hvw uzv
+aoz: cyk qhr scn jex pcv
+dot: kxu
+nbx: ffq ahp owr vvs
+dka: ksc bcv
+yej: nbx hpk fqp uub
+glt: lin jrw
+hbq: wjk you
+nja: mqk dmr
+nct: you eax
+mqk: cyw djr
+lfw: svi
+iyq: xdw rvx bcv
+wcr: iwz
+pkc: ron pst wte qug qee
+ehv: gst ibw knv
+uzv: abn nfd
+tiv: szt
+iii: mbl asl
+eok: eax you wjk
+fvh: mnp
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+qza: bor uzm kpa rgp
+xxj: jec
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+vir: hak yog syp
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+tby: vwm zet
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+kpa: imz zbi mym paz
+cgk: scz
+dpx: tuv sxv lyw
+rgp: paz imz
+eqf: ubs bsf
+lxi: out
+uun: ngl
+kvl: out
+dbb: tcu lwr tby uwx cfq ozk oci uyd xft
+pzz: dbb kma
+xkm: kkq
+edy: luf
+unh: bkp
+yao: xjx
+wvx: wbz woh coz
+dwd: qbe
+egm: iyk xmy
+udo: wte qug ron
+iiy: qgm
+qpx: ert kxk djr
+zwd: ivr wij
+nkk: qgm vdm iwz
+axt: acu jhf
+jxo: cyw djr
+dha: pxu
+mbf: foq tuz qwi onp dot
+lbl: yog
+xka: qif ilb mpt
+ads: abn xeq ilf
+xft: zet ejh vwm
+fbn: eok ntb
+uqr: lfr
+omm: xnb cph ahy
+ecu: szt tvt vzw
+urh: tur xqs
+mym: ivr wij nzf
+ebh: pst qee qug wte
+wxd: ebh tps
+sbj: ert
+neg: oto odt
+kxu: wtr ywu
+dsk: dac chh
+ron: wjk
+ust: you eax
+tsv: pxt mnh fpk
+wij: shp oeb xsp zna sib rpi wql isk eeb xch suw wxd faw gio bik ouk ykl
+hog: ezs gju ibu
+mbl: kma dbb
+hbv: fgn azo
+gdo: kma dbb mup
+vlm: wee mhu
+gis: sxp jhg par xkt
+ohd: eok
+ivr: oeb zna gio tkm sib shp isk bik
+por: pdp qcy lfr
+mrd: gvm
+arh: uwd mlo gao
+loi: iii gxe bkg
+mpe: fqp hpk nbx dcb
+bue: sxp jhg xkt par
+bry: gom etk yqx yao wcs
+bgu: qxf fgq
+jsl: out
+ejh: svp zlg