Saves

Author: romellem

2019/16/part-one.js

@@ -1,30 +1,47 @@
-const { input, inputTimes10 } = require('./input');
+const { input } = require('./input');
 
-const base_pattern = [0, 1, 0, -1];
-let current = inputTimes10;
+var fillPattern = (function () {
+	let cachedPatterns = {};
+
+	return (n) => {
+		if (cachedPatterns[n]) {
+			return cachedPatterns[n];
+		}
+
+		let pattern = [];
+		for (let num of [0, 1, 0, -1]) {
+			for (let i = 0; i < n; i++) {
+				pattern.push(num);
+			}
+		}
+
+		// Offset the whole pattern left by one
+		let first_digit = pattern.shift();
+		pattern.push(first_digit);
+
+		cachedPatterns[n] = pattern;
+
+		return pattern;
+	};
+})();
+
+let current = input;
 
 for (let phase = 1; phase <= 100; phase++) {
 	let new_arr = [];
 	for (let n = 0; n < current.length; n++) {
+		let pattern = fillPattern(n + 1);
 		let sum = 0;
-
-		let index = 0;
-		let position = n + 1;
 		for (let i = 0; i < current.length; i++) {
-			position--;
-			if (position <= 0) {
-				position = n + 1;
-				index = (index + 1) % base_pattern.length;
-			}
-
 			let v = current[i];
-			let scalar = base_pattern[index];
-			let new_val = v * scalar;
+			let index = i % pattern.length;
+			let new_val = v * pattern[index];
 
 			sum += new_val;
 		}
 
-		let last_digit = Math.abs(sum % 10);
+		let last_char = String(sum).substr(-1, 1);
+		let last_digit = parseInt(last_char, 10);
 
 		new_arr.push(last_digit);
 	}

2019/16/part-two.js

@@ -1 +1,11 @@
-const { input } = require('./input');
+const { partTwoInput } = require('./input');
+
+const offset = parseInt(partTwoInput.slice(0, 7).join(''), 10);
+const slice_to_iterate = partTwoInput.slice(offset);
+for (let j = 0; j < 100; j++) {
+	for (let i = slice_to_iterate.length - 2; i >= 0; i--) {
+		slice_to_iterate[i] = (slice_to_iterate[i + 1] + slice_to_iterate[i]) % 10;
+	}
+}
+
+console.log('8 digits:', slice_to_iterate.slice(0, 8).join(''));