2021-advent-10.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"sort"
	"strings"
)

func readLines(input string) []string {
	bytes, err := ioutil.ReadFile(input)
	if err != nil {
		log.Fatal(err)
	}
	lines := append(make([]string, 0, 32), strings.Split(string(bytes), "\n")...)
	return lines
}

type Chunk struct {
	char rune
	prev *Chunk
}

var scoring = map[rune]int{
	')': 3,
	']': 57,
	'}': 1197,
	'>': 25137,
}

// Returns error score or Chunk
func countErrorScore(line string) (*Chunk, int) {

	mapping := map[rune]rune{
		']': '[',
		')': '(',
		'}': '{',
		'>': '<',
	}

	var chunk *Chunk = nil

	for _, rune := range line {
		switch rune {
		case '[', '(', '{', '<':
			newChunk := Chunk{char: rune, prev: chunk}
			chunk = &newChunk
		case ']', ')', '}', '>':
			if chunk == nil {
				// fmt.Printf("Wrong closing %v\n", string(rune))
				return nil, scoring[rune]
			}
			if mapping[rune] == chunk.char {
				chunk = chunk.prev
			} else {
				// fmt.Printf("Wrong closing %v\n", string(rune))
				return nil, scoring[rune]
			}
		default:
			fmt.Printf("Wrong input: %v\n", rune)
		}
	}
	// fmt.Printf("Ok line: %s\n", line)
	return chunk, 0
}

func Task1(input string) {
	lines := readLines(input)
	counter := 0
	for _, line := range lines {
		_, score := countErrorScore(line)
		counter += score
	}
	fmt.Printf("Day10 Task1 %s: %v\n", input, counter)
}

func findCompletion(chunk *Chunk) string {

	mapping := map[rune]rune{
		'[': ']',
		'(': ')',
		'{': '}',
		'<': '>',
	}

	tmp_chunk := chunk
	agg := ""
	for tmp_chunk != nil {
		agg += string(mapping[tmp_chunk.char])
		tmp_chunk = tmp_chunk.prev
	}
	return agg
}

func scoreCompletion(completion string) int {
	score := 0
	for _, rune := range completion {
		score *= 5
		switch rune {
		case ')':
			score += 1
		case ']':
			score += 2
		case '}':
			score += 3
		case '>':
			score += 4
		}
	}
	return score
}

func Task2(input string) {
	lines := readLines(input)
	scores := make([]int, 0)
	for _, line := range lines {
		chunk, errScore := countErrorScore(line)
		if errScore > 0 {
			//skip lines with error
			continue
		}
		completion := findCompletion(chunk)
		score := scoreCompletion(completion)
		scores = append(scores, score)
		// fmt.Printf("%s - %d\n", completion, score)
	}
	sort.Ints(scores)
	// fmt.Printf("Scores %v\n", scores)
	winningScore := scores[len(scores)/2]
	fmt.Printf("Day10 Task2 %s: %v\n", input, winningScore)
}

func main() {
	Task1("example.txt")
	Task1("input.txt")
	Task2("example.txt")
	Task2("input.txt")
}