AdventOfCode2022/07/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

func mustAtoi(line string) int {
	i, _ := strconv.Atoi(line)
	return i
}

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

type Folder struct {
	name    string
	files   map[string]int
	folders map[string]*Folder
	size    int
}

func partOne() {
	scanner := makeScanner(false)

	root := Folder{
		name:    "/",
		files:   map[string]int{},
		folders: map[string]*Folder{},
	}
	sum := 0
	stack := []*Folder{&root}
	for scanner.Scan() {
		line := scanner.Text()
		switch {
		case line == "$ cd /": // don't care
			continue
		case line == "$ ls": // definitely don't care
			continue
		case line == "$ cd ..":
			// since we're done in that child, compute it's size.
			curr := stack[len(stack)-1]
			for _, size := range curr.files {
				curr.size += size
			}
			for _, f := range curr.folders {
				curr.size += f.size
			}
			if curr.size <= 100000 {
				sum += curr.size
			}
			// pop off stack
			stack = stack[0 : len(stack)-1]
		case strings.HasPrefix(line, "$ cd "): // descend into folder
			stack = append(stack, stack[len(stack)-1].folders[strings.Split(line, " ")[2]])
		case strings.HasPrefix(line, "dir "): // add directory to current folder
			name := strings.Split(line, " ")[1]
			stack[len(stack)-1].folders[name] = &Folder{
				name:    name,
				files:   map[string]int{},
				folders: map[string]*Folder{},
			}
		default: // add file to current folder
			stack[len(stack)-1].files[strings.Split(line, " ")[1]] = mustAtoi(strings.Split(line, " ")[0])
		}
	}
	// finish computing directory sizes
	for len(stack) > 0 {
		curr := stack[len(stack)-1]
		for _, size := range curr.files {
			curr.size += size
		}
		for _, f := range curr.folders {
			curr.size += f.size
		}
		stack = stack[0 : len(stack)-1]
	}
	fmt.Println(sum)
}

func partTwo() {
	scanner := makeScanner(false)

	root := Folder{
		name:    "/",
		files:   map[string]int{},
		folders: map[string]*Folder{},
	}
	spaceToFree := 30000000 - (70000000 - 49192532) // size of all files, precomputed
	toDelete := 70000000
	stack := []*Folder{&root}
	for scanner.Scan() {
		line := scanner.Text()
		switch {
		case line == "$ cd /": // don't care
			continue
		case line == "$ ls": // definitely don't care
			continue
		case line == "$ cd ..":
			// since we're done in that child, compute it's size.
			curr := stack[len(stack)-1]
			for _, size := range curr.files {
				curr.size += size
			}
			for _, f := range curr.folders {
				curr.size += f.size
			}
			if curr.size > spaceToFree && curr.size < toDelete {
				toDelete = curr.size
			}
			// pop off stack
			stack = stack[0 : len(stack)-1]
		case strings.HasPrefix(line, "$ cd "): // descend into folder
			stack = append(stack, stack[len(stack)-1].folders[strings.Split(line, " ")[2]])
		case strings.HasPrefix(line, "dir "): // add directory to current folder
			name := strings.Split(line, " ")[1]
			stack[len(stack)-1].folders[name] = &Folder{
				name:    name,
				files:   map[string]int{},
				folders: map[string]*Folder{},
			}
		default: // add file to current folder
			stack[len(stack)-1].files[strings.Split(line, " ")[1]] = mustAtoi(strings.Split(line, " ")[0])
		}
	}
	// finish computing directory sizes
	for len(stack) > 0 {
		curr := stack[len(stack)-1]
		for _, size := range curr.files {
			curr.size += size
		}
		for _, f := range curr.folders {
			curr.size += f.size
		}
		if curr.size > spaceToFree && curr.size < toDelete {
			toDelete = curr.size
		}
		stack = stack[0 : len(stack)-1]
	}
	fmt.Println(toDelete)
}