Day 9

day9.peggy

@@ -0,0 +1,3 @@
+lines = @num+ "\n"
+
+num = n:$[0-9] { return parseInt(n, 10) }

day9.ts

@@ -0,0 +1,114 @@
+import { type MainArgs, parseFile } from './lib/utils.ts';
+
+type Parsed = number[];
+
+function genBlocks(inp: Parsed): [blocks: number[], file: number] {
+  const blocks: number[] = [];
+  let file = 0;
+  let free = false;
+  let block = 0;
+  for (const n of inp) {
+    if (free) {
+      for (let i=0; i<n; i++) {
+        blocks[block++] = NaN;
+      }
+    } else {
+      for (let i=0; i<n; i++) {
+        blocks[block++] = file;
+      }
+      file++;
+    }
+    free = !free;
+  }
+
+  return [blocks, file - 1];
+}
+
+function part1(inp: Parsed): number {
+  const [blocks, maxFile] = genBlocks(inp);
+  let file = maxFile;
+  let i = 0;
+  let j = blocks.length - 1;
+  while (i < j) {
+    while (i < j) {
+      if (isNaN(blocks[i])) {
+        break;
+      }
+      i++;
+    }
+    while (j > i) {
+      file = blocks[j];
+      delete blocks[j];
+      if (!isNaN(file)) {
+        break;
+      }
+      j--;
+    }
+    if (i < j) {
+      blocks[i] = file;
+    } else {
+      break;
+    }
+  }
+
+  return blocks.reduce((t, v, n) => t + (v === undefined ? 0 : v * n), 0);
+}
+
+function part2(inp: Parsed): number {
+  const [blocks, maxFile] = genBlocks(inp);
+  let initial = 0;
+
+  for (let file = maxFile; file >= 0; file--) {
+    // TODO: move to lastIndexOf
+    const start = blocks.indexOf(file, initial);
+    if (start === -1) {
+      continue;
+    }
+    let end = start;
+    while (end < blocks.length) {
+      if (blocks[++end] !== file) {
+        break;
+      }
+    }
+
+    const len = end - start;
+    let i = initial;
+    initial = NaN;
+
+    OUTER:
+    while (i < start) {
+      while (i < start) {
+        if (isNaN(blocks[i])) {
+          if (isNaN(initial)) {
+            initial = i;
+          }
+          break;
+        }
+        i++;
+      }
+      if (i < start) {
+        for (let x = i; x < i + len; x++) {
+          if (!isNaN(blocks[x])) {
+            i = x;
+            continue OUTER;
+          }
+        }
+        break;
+      }
+    }
+    if (i < start) {
+      for (let x = i; x < i + len; x++) {
+        blocks[x] = file;
+        blocks[start + x - i] = NaN;
+      }
+      i += len;
+    }
+  }
+
+  return blocks.reduce((t, v, n) => t + (isNaN(v) ? 0 : v * n), 0);
+}
+
+export default async function main(args: MainArgs): Promise<[number, number]> {
+  const inp = await parseFile<Parsed>(args);
+  return [part1(inp), part2(inp)];
+}

test/day9.js

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+export default [6301895872542, 6323761685944];