AdventOfCode2021/10/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
	"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 parsed struct {
	errorChar         rune
	missingkeys       []rune
	autocompleteTotal int
}

func pop(stack []rune) (rune, []rune) {
	pop := stack[len(stack)-1]
	return pop, stack[:len(stack)-1]
}

func parseLine(line string) parsed {
	stack := []rune{}
	for _, v := range line {
		var p rune
		switch v {
		case '[', '{', '<', '(':
			stack = append(stack, v)
		case '>':
			p, stack = pop(stack)
			if p != '<' {
				return parsed{errorChar: v}
			}
		case ')':
			p, stack = pop(stack)
			if p != '(' {
				return parsed{errorChar: v}
			}
		case ']':
			p, stack = pop(stack)
			if p != '[' {
				return parsed{errorChar: v}
			}
		case '}':
			p, stack = pop(stack)
			if p != '{' {
				return parsed{errorChar: v}
			}
		}
	}
	if len(stack) != 0 {
		return parsed{missingkeys: stack}
	}
	return parsed{}
}

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

	sum := 0
	for scanner.Scan() {
		result := parseLine(scanner.Text())
		switch result.errorChar {
		case ')':
			sum += 3
		case ']':
			sum += 57
		case '}':
			sum += 1197
		case '>':
			sum += 25137
		}
	}
	fmt.Println(sum)
}

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

	scores := []int{}
	for scanner.Scan() {
		result := parseLine(scanner.Text())
		if result.errorChar == 0 {
			for i := len(result.missingkeys) - 1; i >= 0; i-- {
				result.autocompleteTotal *= 5
				switch result.missingkeys[i] {
				case '(':
					result.autocompleteTotal += 1
				case '[':
					result.autocompleteTotal += 2
				case '{':
					result.autocompleteTotal += 3
				case '<':
					result.autocompleteTotal += 4
				}
			}
			scores = append(scores, result.autocompleteTotal)
		}
	}
	sort.Ints(scores)
	fmt.Println(scores[(len(scores) / 2)])
}