Generating 20 generations from the input looks like this:

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Generating 20 generations from the input looks like this:

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let plantTracker = new Plants(initialState, rules)

// Start for part 2

const generations2 = 500

for (let gen = generations + 1; gen <= generations2; gen++) {

plantTracker.advance()

}

console.log(`Generating ${generations2} generations from the input looks like this:`)

plantTracker.display()

// 500 generations takes about 30s, so running 50B generations isn't possible. It's

// clear looking at the log there's a "Game of Life"-style glider.

// See output/500-generations.txt and output/500-generations.png

// This probably is reflected in a pattern in the checksum.

let prevCheckSum = 0

let prevDelta = 0

const stableThreshold = 5 // The number of sequentially identical deltas necessary to determine stabilization

const stableDeltas = Array(stableThreshold).fill(0)

let stableGeneration = 0

let stableCheckSum = 0

for (let gen = 0; gen <= generations2; gen++) {

const checkSum = plantTracker.getCheckSum(gen)

const delta = checkSum - prevCheckSum

console.log(`Generation ${gen} checksum: ${plantTracker.getCheckSum(gen)} which is Δ of ${delta})`)

// When delta matches previous generation, we may have reached stabilization

if (delta === prevDelta) {

stableDeltas.shift()

stableDeltas.push(delta)

// Reached true stable point when there are N deltas in a row that are the same.

if (stableDeltas.filter((Δ) => Δ === delta).length === stableDeltas.length) {

stableCheckSum = checkSum

stableGeneration = gen

break

}

}

prevCheckSum = checkSum

prevDelta = delta

}

console.log(`At generation ${stableGeneration} the Δ is ${stableDeltas[0]} and the checksum is ${stableCheckSum}.`)

// Calculate the checksum for 50B generations (minus the generation we're already at)

const answer2 = (stableDeltas[0] * (50000000000 - stableGeneration - 1)) + stableCheckSum