aoc2023/day-5/two.go

package main

import (
	"math"
	"sync"
)

var wg sync.WaitGroup
var mu sync.Mutex

const UNLIMITED = -1

// bound represents the lower and upper limits of a single range
type bound struct {
	lower, upper int
}

// newBound returns a bound type
// it defines an open ended interval
func newBound(lower, upper int) bound {
	return bound{lower: lower, upper: upper - 1}
}

// nextTransform recursively calculates each new set of seed ranges for each set of data in dataMap
func nextTransform(i int, in []bound) []bound {
	if i == len(identifiers) {
		return in
	}

	q := newQueue(UNLIMITED, in)
	in = make([]bound, 0)
	for !q.isEmpty() {
		r := q.dequeue()

		hasOverlap := func() bool {
			for _, data := range dataMap[identifiers[i]] {
				start := max(r.lower, data.source)
				end := min(r.upper, data.source+data.offset)

				if isOverlapping(start, end) {
					// add new seed range
					in = append(in, newBound(data.transform(start, end)))

					// append unmatched portions of seed range back into queue
					if start > r.lower {
						q.enqueue(newBound(r.lower, start))
					}
					if r.upper > end {
						q.enqueue(newBound(end, r.upper))
					}
					return true
				}
			}
			return false
		}()

		// there was no overlap, add the seed range as is
		if !hasOverlap {
			in = append(in, r)
		}
	}

	return nextTransform(i+1, in)
}

// two returns the lowest location for any seed in seedRanges
func two(lines []string) int {
	var seedRanges = []bound{}
	for i := 0; i < len(seeds); i += 2 {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			mu.Lock()
			seedRanges = append(seedRanges, nextTransform(0, []bound{newBound(seeds[i], seeds[i]+seeds[i+1])})...)
			mu.Unlock()
		}(i)
	}

	wg.Wait()

	lowest := math.MaxInt
	for _, r := range seedRanges {
		if r.lower < lowest {
			lowest = r.lower
		}
	}

	return lowest
}