2024 Day 09

2024/d09/index.ts

@@ -0,0 +1,119 @@
+import { readFileSync } from 'node:fs'
+
+import { runExamples, runSolution } from '@magiczne/advent-of-code-ts-core/aoc'
+
+const EMPTY = -1
+
+const part1 = (data: ReadonlyArray<number>): number => {
+  let currentFileId = 0
+  const disk: Array<number> = []
+
+  for (let i = 0; i < data.length; i++) {
+    const isEmpty = i % 2 !== 0
+    const value = isEmpty ? EMPTY : currentFileId
+
+    disk.push(...Array.from({ length: data[i] }, _ => value))
+
+    if (!isEmpty) {
+      currentFileId++
+    }
+  }
+
+  for (let i = disk.length - 1; i >= 0; i--) {
+    if (disk[i] === EMPTY || disk.indexOf(EMPTY) > i) {
+      continue
+    }
+
+    disk[disk.indexOf(EMPTY)] = disk[i]
+    disk[i] = EMPTY
+  }
+
+  return disk.reduce((acc, item, index) => {
+    if (item === EMPTY) {
+      return acc
+    }
+
+    return acc + index * item
+  }, 0)
+}
+
+const part2 = (data: ReadonlyArray<number>): number => {
+  let currentFileId = 0
+  let disk: Array<{ id: number; length: number }> = data.map((item, index) => {
+    const isEmpty = index % 2 !== 0
+    const id = isEmpty ? EMPTY : currentFileId++
+
+    if (isEmpty) {
+      return { id, length: item }
+    }
+
+    return {
+      id,
+      length: item,
+    }
+  })
+
+  for (let i = currentFileId - 1; i >= 0; i--) {
+    const fileIndex = disk.findIndex(block => block.id === i)
+    const freeSpaceIndex = disk.findIndex(block => block.id === EMPTY && block.length >= disk[fileIndex].length)
+
+    if (freeSpaceIndex === -1 || fileIndex < freeSpaceIndex) {
+      continue
+    }
+
+    if (disk[freeSpaceIndex].length > disk[fileIndex].length) {
+      disk = [
+        ...disk.slice(0, freeSpaceIndex),
+        { id: disk[fileIndex].id, length: disk[fileIndex].length },
+        { id: EMPTY, length: disk[freeSpaceIndex].length - disk[fileIndex].length },
+        ...disk.slice(freeSpaceIndex + 1),
+      ]
+      disk[fileIndex + 1].id = EMPTY
+    } else if (disk[freeSpaceIndex].length === disk[fileIndex].length) {
+      disk[freeSpaceIndex].id = disk[fileIndex].id
+      disk[fileIndex].id = EMPTY
+    }
+  }
+
+  // There may be places with two empty blocks next to each other, we need to compact them
+  for (let j = 0; j < disk.length - 1; j++) {
+    if (disk[j].id == EMPTY && disk[j + 1].id == EMPTY) {
+      disk = [...disk.slice(0, j), { id: EMPTY, length: disk[j].length + disk[j + 1].length }, ...disk.slice(j + 2)]
+
+      j--
+    }
+  }
+
+  return disk.reduce(
+    (acc, block) => {
+      if (block.id === EMPTY) {
+        return {
+          blockId: acc.blockId + block.length,
+          checksum: acc.checksum,
+        }
+      }
+
+      return {
+        blockId: acc.blockId + block.length,
+        checksum:
+          acc.checksum +
+          Array.from({ length: block.length }, (_, index) => {
+            return block.id * (index + acc.blockId)
+          }).reduce((blockAcc, value) => blockAcc + value, 0),
+      }
+    },
+    { blockId: 0, checksum: 0 },
+  ).checksum
+}
+
+const reader = (file: string): ReadonlyArray<number> => {
+  return readFileSync(file, 'utf-8')
+    .trim()
+    .split('')
+    .map(item => {
+      return parseInt(item, 10)
+    })
+}
+
+runExamples(2024, '09', reader, part1, part2)
+runSolution(2024, '09', reader, part1, part2)