Parnic
f03184d4c4
This one's part 1 destroyed me. I had a very difficult time, trying 3 separate approaches, each one of which worked for most cases but eventually fell apart on the 5th sample or my actual puzzle input. I ended up reading a bunch of hints from the subreddit which eventually led me to a blog post describing this solution, which wasn't far off from what I had, but I was overcomplicating things. Part 2 surprised me in that I expected a simple "ore available divided by ore needed for 1 fuel" would solve it, but of course the excess chemicals produced in any given reaction meant that it wasn't that simple. So this approach uses that estimate as a lower bound, since it always underestimates, and then bisects its way to the solution (starting at the lower bound and adding 1 each time took too long). I'm sure a smarter upper bound choice could lower the runtime of this by a bit, but runtime isn't bad enough right now for me to try any additional optimizations.
130 lines
2.8 KiB
Go
130 lines
2.8 KiB
Go
package days
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import (
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"fmt"
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"math"
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"strconv"
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"strings"
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u "parnic.com/aoc2019/utilities"
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)
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type reaction struct {
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inputs map[string]int64
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output u.Pair[string, int]
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}
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type Day14 struct {
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reactions []reaction
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}
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func (d *Day14) Parse() {
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lines := u.GetStringLines("14p")
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d.reactions = make([]reaction, len(lines))
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for i, line := range lines {
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sides := strings.Split(line, " => ")
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inputs := strings.Split(sides[0], ", ")
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output := sides[1]
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outPair := strings.Split(output, " ")
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outAmt, _ := strconv.Atoi(outPair[0])
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d.reactions[i].output = u.Pair[string, int]{First: outPair[1], Second: outAmt}
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d.reactions[i].inputs = make(map[string]int64)
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for _, input := range inputs {
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pair := strings.Split(input, " ")
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d.reactions[i].inputs[pair[1]], _ = strconv.ParseInt(pair[0], 10, 64)
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}
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}
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}
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func (d Day14) getReactionProducing(chem string) *reaction {
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for _, reaction := range d.reactions {
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if reaction.output.First == chem {
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return &reaction
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}
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}
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return nil
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}
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func (d Day14) Num() int {
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return 14
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}
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func (d *Day14) getOreRequiredForFuel(qty int64) int64 {
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oreRequired := int64(0)
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needs := map[string]int64{
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"FUEL": qty,
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}
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excess := make(map[string]int64)
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getFromExcess := func(qty int64, chemical string) int64 {
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available := u.Min(excess[chemical], qty)
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excess[chemical] -= available
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return available
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}
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for len(needs) > 0 {
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keys := u.MapKeys(needs)
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producing := keys[0]
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qtyRequired := needs[producing]
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delete(needs, producing)
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fromExcess := getFromExcess(qtyRequired, producing)
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if fromExcess == qtyRequired {
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continue
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}
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qtyRequired -= fromExcess
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reaction := d.getReactionProducing(producing)
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qtyProduced := int64(reaction.output.Second)
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reactionsNeeded := int64(math.Ceil(float64(qtyRequired) / float64(qtyProduced)))
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excess[producing] = (qtyProduced * reactionsNeeded) - qtyRequired
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for reagent, inputQty := range reaction.inputs {
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qtyNeeded := inputQty * reactionsNeeded
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if reagent == "ORE" {
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oreRequired += qtyNeeded
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} else {
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needs[reagent] += qtyNeeded
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}
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}
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}
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return oreRequired
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}
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func (d *Day14) Part1() string {
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neededOre := d.getOreRequiredForFuel(1)
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return fmt.Sprintf("%s%d%s", u.TextBold, neededOre, u.TextReset)
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}
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func (d *Day14) Part2() string {
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oreAvailable := int64(1000000000000)
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estimate := oreAvailable / d.getOreRequiredForFuel(1)
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high := estimate * 2
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low := estimate
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lastSuccess := low
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lastFailure := high
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fuelProduced := low
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for math.Abs(float64(lastFailure-lastSuccess)) > 1 {
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oreConsumed := d.getOreRequiredForFuel(fuelProduced)
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adjustment := (lastFailure - lastSuccess) / 2
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if oreConsumed < oreAvailable {
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lastSuccess = fuelProduced
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} else {
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lastFailure = fuelProduced
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adjustment = -adjustment
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}
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fuelProduced += adjustment
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}
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return fmt.Sprintf("%s%d%s", u.TextBold, lastSuccess, u.TextReset)
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}
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