feat(js): add solutions for 2023 day 9

js/src/2023/09/index.js

@@ -0,0 +1,47 @@
+import { cast, solution, sum } from '../../utils';
+
+const parse = (input) => (
+  input.trim().split('\n').map((line) => line.split(' ').map(cast))
+);
+
+const isZero = (value) => value === 0;
+
+const derive = (sequence) => {
+  const lastIndex = sequence.length - 1;
+  return sequence.reduce((list, current, index) => {
+    const next = sequence.at(index + 1);
+    if (index !== lastIndex) {
+      list.push(next - current);
+    }
+    return list;
+  }, []);
+};
+
+const extend = (sequence, append = true) => {
+  let value = 0;
+  if (!sequence.every(isZero)) {
+    const derivation = derive(sequence);
+    const extended = extend(derivation, append);
+    value = append ? sequence.at(-1) + extended.at(-1) : sequence.at(0) - extended.at(0);
+  }
+
+  const next = [...sequence];
+  if (append) {
+    next.push(value);
+  } else {
+    next.unshift(value);
+  }
+  return next;
+};
+
+export const partOne = solution((input) => {
+  const sequences = parse(input);
+  const extended = sequences.map((seq) => extend(seq));
+  return sum(extended.map((sequence) => sequence.at(-1)));
+});
+
+export const partTwo = solution((input) => {
+  const sequences = parse(input);
+  const extended = sequences.map((seq) => extend(seq, false));
+  return sum(extended.map((sequence) => sequence.at(0)));
+});

puzzles/2023/09/examples.yaml

@@ -0,0 +1,10 @@
+part-one:
+  - input: &example1 |
+      0 3 6 9 12 15
+      1 3 6 10 15 21
+      10 13 16 21 30 45
+    answer: 114
+
+part-two:
+  - input: *example1
+    answer: 2