day01.go

package main

import (
	_ "embed"
	"fmt"
	"strings"
)

//go:embed input.txt
var input string

func part1(input string) int {
	lines := strings.Split(input, "\n")

	var first, last, sum int
	for _, line := range lines {
		for i := range line {
			if line[i] >= '1' && line[i] <= '9' {
				first = int(line[i] - '0')
				break
			}
		}

		for i := len(line) - 1; i >= 0; i-- {
			if line[i] >= '1' && line[i] <= '9' {
				last = int(line[i] - '0')
				break
			}
		}

		sum += first*10 + last
	}

	return sum
}

func part2(input string) int {
	lines := strings.Split(input, "\n")
	digits := []string{"one", "two", "three", "four", "five", "six", "seven", "eight", "nine"}

	var first, last, sum int
	for _, line := range lines {
	FirstLoop:
		for i := 0; i < len(line); i++ {
			b := line[i]
			if b >= '1' && b <= '9' {
				first = int(b - '0')
				break
			}

			if b == 'e' || b == 'f' || b == 'n' || b == 'o' || b == 's' || b == 't' {
				for j, digit := range digits {
					for k := 0; line[i+k] == digit[k]; k++ {
						if len(digit)-1 == k {
							first = j + 1
							break FirstLoop
						}
					}
				}
			}
		}

	LastLoop:
		for i := len(line) - 1; i >= 0; i-- {
			b := line[i]
			if b >= '1' && b <= '9' {
				last = int(b - '0')
				break
			}

			if b == 'e' || b == 'n' || b == 'o' || b == 'r' || b == 't' || b == 'x' {
				for j, digit := range digits {
					for k := 0; line[i-k] == digit[len(digit)-1-k]; k++ {
						if len(digit)-1 == k {
							last = j + 1
							break LastLoop
						}
					}
				}
			}
		}

		sum += first*10 + last
	}

	return sum
}

func main() {
	fmt.Println("--- 2023 day 01 answer ---")
	fmt.Println("part 1:\t", part1(input))
	fmt.Println("part 2:\t", part2(input))
}