AdventOfCode2023/05/main.go

package main

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

func must[T, Q any](f func(T) (Q, error), t T) Q {
	q, err := f(t)
	if err != nil {
		panic(err)
	}
	return q
}

func iter[T, Q any](f func(T) Q, t []T) []Q {
	r := make([]Q, len(t))
	for i := 0; i < len(t); i++ {
		r[i] = f(t[i])
	}
	return r
}

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)
}

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

	seeds := [][]int{}
	scanner.Scan()
	line := scanner.Text()
	_, seedList, _ := strings.Cut(line, ": ")
	for _, s := range strings.Split(seedList, " ") {
		seeds = append(seeds, []int{must(strconv.Atoi, s)})
	}
	scanner.Scan() // discard empty line

	state := 1
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			for i, s := range seeds {
				if len(s) == state {
					seeds[i] = append(seeds[i], s[state-1])
				}
			}
			state++
			continue
		}
		if line[len(line)-1] == ':' {
			continue
		}
		// destination, source, length
		m := iter(
			func(s string) int { return must(strconv.Atoi, s) },
			strings.Split(line, " "),
		)
		for i, s := range seeds {
			if len(s) == state && m[1] <= s[state-1] && m[1]+m[2] > s[state-1] {
				seeds[i] = append(seeds[i], s[state-1]-m[1]+m[0])
			}
		}
	}
	lowest := seeds[0][len(seeds[0])-1]
	for _, s := range seeds {
		if s[len(s)-1] < lowest {
			lowest = s[len(s)-1]
		}
	}
	fmt.Println(lowest)
}

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

	seeds := [][]int{}
	scanner.Scan()
	line := scanner.Text()
	_, seedRanges, _ := strings.Cut(line, ": ")
	r := strings.Split(seedRanges, " ")
	for i := 0; i <= len(r); i += i + 2 {
		rng := must(strconv.Atoi, r[i+1])
		for j := 0; j < rng; j++ {
			// this is too slow!
			seeds = append(seeds, []int{must(strconv.Atoi, r[i]) + j})
		}
	}
	scanner.Scan() // discard empty line

	state := 1
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			for i, s := range seeds {
				if len(s) == state {
					seeds[i] = append(seeds[i], s[state-1])
				}
			}
			state++
			continue
		}
		if line[len(line)-1] == ':' {
			continue
		}
		// destination, source, length
		m := iter(
			func(s string) int { return must(strconv.Atoi, s) },
			strings.Split(line, " "),
		)
		for i, s := range seeds {
			if len(s) == state && m[1] <= s[state-1] && m[1]+m[2] > s[state-1] {
				seeds[i] = append(seeds[i], s[state-1]-m[1]+m[0])
			}
		}
	}
	lowest := seeds[0][len(seeds[0])-1]
	for _, s := range seeds {
		if s[len(s)-1] < lowest {
			lowest = s[len(s)-1]
		}
	}
	fmt.Println(lowest)
}