Solution for day 15 (2020)

Author: joshthompson

2020/15/index.js

@@ -0,0 +1,16 @@
+const numbers = '14,3,1,0,9,5'.split(',').map(Number)
+
+console.log('Part 1', run(numbers, 2020))
+console.log('Calculating... (Part 2 takes 5-10 seconds to run)')
+console.log('Part 2', run(numbers, 30000000))
+
+function run(numbers, total) {
+	const occurances = new Map()
+	let next = 0
+	for (let i = 0; i < total; i++) {
+		if (numbers[i] === undefined) numbers[i] = next
+		next = occurances.get(numbers[i]) !== undefined ? i - occurances.get(numbers[i]) : 0
+		occurances.set(numbers[i], i)
+	}
+	return numbers[numbers.length - 1]
+}