advent-of-code/aoc2024/day01/main.go

package main

import (
	"bufio"
	_ "embed"
	"fmt"
	"iter"
	"slices"
	"sort"

	aoc "go.sour.is/advent-of-code"
)

// var log = aoc.Log

func main() { aoc.MustResult(aoc.Runner(run)) }

type result struct {
	valuePT1 int
	valuePT2 int
}

func (r result) String() string { return fmt.Sprintf("%#v", r) }

func run(scan *bufio.Scanner) (*result, error) {
	var (
		left  []int
		right []int
	)

	for scan.Scan() {
		txt := scan.Text()

		var l, r int
		_, err := fmt.Sscanf(txt, "%d %d", &l, &r)
		if err != nil {
			return nil, err
		}

		left = append(left, l)
		right = append(right, r)
	}

	sort.Ints(left)
	sort.Ints(right)

	result := &result{}

	result.valuePT1 = aoc.Reduce(func(i int, z pair[int, int], sum int) int {
		return sum + aoc.ABS(z.L-z.R)
	}, 0, zip(slices.Values(left), slices.Values(right)))

	rmap := aoc.Reduce(func(i int, z int, m map[int]int) map[int]int {
		m[z]++
		return m
	}, make(map[int]int), slices.Values(right))
	
	for _, v := range left {
		if r, ok := rmap[v]; ok {	
			result.valuePT2 += v*r
		}
	}

	return result, nil
}

type pair[L, R any] struct {
	L L
	R R
}

func zip[L, R any](l iter.Seq[L], r iter.Seq[R]) iter.Seq[pair[L,R]] {
	return func(yield func(pair[L, R]) bool) {
		pullR, stop := iter.Pull(r)
		defer stop()

		for l := range l {
			r, _ := pullR()

			if !yield(pair[L, R]{L: l, R: r}) {
				return
			}
		}
	}
}