adventofcode2023/day01.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"strconv"
	"strings"
	"unicode"
)

func linevalue(digits []rune) int {
	str := fmt.Sprintf("%c%c", digits[0], digits[len(digits)-1])
	value, _ := strconv.Atoi(str)
	return value
}

func finddigits(line string) []rune {
	d := make([]rune, 0, 7)
	for len(line) > 0 {
		if unicode.IsDigit(rune(line[0])) {
			d = append(d, rune(line[0]))
		}
		line = line[1:]
	}
	return d
}

func findtextdigits(line string) []rune {
	d := make([]rune, 0, 7)
	for len(line) > 0 {
		if unicode.IsDigit(rune(line[0])) {
			d = append(d, rune(line[0]))
		}

		if strings.HasPrefix(line, "one") {
			d = append(d, '1')
			line = line[2:]
		} else if strings.HasPrefix(line, "two") {
			d = append(d, '2')
			line = line[2:]
		} else if strings.HasPrefix(line, "three") {
			d = append(d, '3')
			line = line[4:]
		} else if strings.HasPrefix(line, "four") {
			d = append(d, '4')
			line = line[4:] // skip len("four") entirely because no digits start with 'r'
		} else if strings.HasPrefix(line, "five") {
			d = append(d, '5')
			line = line[3:]
		} else if strings.HasPrefix(line, "six") {
			d = append(d, '6')
			line = line[3:] // skip len("six") entirely because no digits start with 'x'
		} else if strings.HasPrefix(line, "seven") {
			d = append(d, '7')
			line = line[4:]
		} else if strings.HasPrefix(line, "eight") {
			d = append(d, '8')
			line = line[4:]
		} else if strings.HasPrefix(line, "nine") {
			d = append(d, '9')
			line = line[3:]
		} else {
			line = line[1:]
		}
	}
	return d
}

type day01 struct {
}

func (d day01) solve1(r io.Reader) string {
	var (
		total   int
		scanner = bufio.NewScanner(r)
	)

	for scanner.Scan() {
		digits := finddigits(scanner.Text())
		total += linevalue(digits)
	}
	return fmt.Sprintf("%d", total)
}

func (d day01) solve2(r io.Reader) (ans string) {
	var (
		total   int
		scanner = bufio.NewScanner(r)
	)

	for scanner.Scan() {
		digits := findtextdigits(scanner.Text())
		total += linevalue(digits)
	}

	return fmt.Sprintf("%d", total)
}